Unfortunately, Civ VI does have some scattered technical problems. I say "unfortunately" because the game itself, - I'll avoid using "perfect", which might suggest that it can not be improved upon - is flawless. Even systems like Diplomacy, where there are some seemingly obvious technical snafus, offer a sturdy foundation, not only for balancing tweaks and DLC for Civ VI, but for the future of the series.
After nearly 120 hours played between the preview and the final build, I can say with confidence that this is my favorite Civ this century. There are some major changes to the game systems that add much to the experience, but it's not just the big stuff that makes this Civ so good. The simpler graphics give you all the information you need without ever distracting you with lighting effects and the like. The city screen was replaced with a small, simple frame that offers the same functionality, only from the world view. Builders replaced Workers, and they don't even have the Build Road ability. Even the core city development system has changed, putting a focus on specialization through the "Districts", such as the Campus, where all of your Science buildings will live. Wonders, on the other hand, will occupy their own tile, and many have heavy restrictions on where they can be placed.
The good of Civ VI far outweighs the bad, but that doesn't mean there aren't some problems worth mentioning. For starters, there are some systems that definitely need to be tweaked, with Diplomacy being the most notable. AI Diplomacy has never been great, admittedly, but in this case, I've had repeated situations where a leader would start taunting me about how my military or science is too weak, despite my having more than twice that of second place. This doesn't have any major impact on the game, but it's indicative of the system's faults. The other major issue with Diplomacy is the Warmongering Penalty, which seems like a strong concept, but currently punishes you for being attacked as much as it does for attacking someone. This may actually be the single biggest issue I have with Civ VI as it stands. Anecdotally, Russia's leader Peter, mentioned above, was at war with virtually every other nation. He was hated for being a warmonger. He had captured at least four different city states. When he attacked me, I took the fight to him, liberated the conquered City State of Toronto and returned it to its rightful owners, captured a small city Russia used as a staging point for the attack on me, and accrued a huge Warmonger penalty with the rest of the world, which eventually ended in them teaming up to attack me, despite my military being, once again, vastly superior to the combined might of the coalition. Suffice to say, Diplomacy doesn't always make much sense here. It's got a great foundation for the concepts with Casus Belli vs Surprise Wars, as well as the warmongering penalty, but there is a lot wrong with the current warmongering scheme, and I shouldn't be punished for defending myself against the dude that's been Blitzkrieging the entire world for 500 years.
More minor, but far more annoying turn-by-turn is that your military can't occupy the same space as other civs' Religious units, so it's possible for non-aggressive civs to accidentally block your armies with their Missionaries, which is magnified by the tendency of the AI to burst with a dozen or so units at the same time, which can stop the most fearsome army in its tracks, unless you don't mind going to war with the religious zealots. I've actually been in situations where that was my only option, since Missionaries had cut off my army from my besieged city, forcing me to cut my way through. Given there's a system in place for Civilian and MIlitary units to share a tile, it seems weird that not murdering your not-enemy's missionary isn't an option.
I hate to have spent so much time talking about the flaws of Civ VI, so let's get into the abundant positives! The massive system changes center around expanding the functions of the city tiles. Your city proper still accommodates some of the most basic structures, like your Granary and Monument. More specialized buildings, like Banks, Libraries, and Factories must be built in their corresponding District. Commercial Hub will give an extra Trade Route, and open up your options for Financial buildings and specialists. Similarly, Industrial Zones allow construction of Workshops and Factories to boost your production. The districts occupy a tile, so positioning can turn out to be very important, so it's wise to plan ahead, at least a bit. The Ruhr Valley wonder, for example, must be constructed adjacent to both a river and an Industrial Zone with a Factory, so you'll need to make sure to plan for it, or you may find yourself in a predicament.
The Districts do require a bit of specialization for up-and-coming cities, but the game doesn't preclude a supercity with every district, as long as there's population enough to support it. At the start, though, each city will largely specialize in whatever complements its geography. A production-light placement means you'll want to focus on growth first, else you'll be waiting a couple dozen turns for your one or two citizens to complete a project. There are some easy ways to supplement construction in this sort of city, though, with Builders able to clear Forest and Rainforest tiles for big chunks of production. If you're struggling to get your production up, this is a great way to bootstrap your city.
Builders replacing Workers is an enormously positive change, and the new units seem to be the natural fit for the role. Instead of having permanent Worker units wandering around, building roads that you can't afford to maintain, or just pulling in a salary with no work to do, Builders are consumable units with a set number of Build actions. Default is three, but Pyramids give you one extra, and there is a Civic Policy that adds two more Builds. Builders never need to build roads, which are created through the Trade Route system, instead focusing on building tile improvements to improve city output. Each improvement costs a Build action, and your Builder will vanish after the last charge is expended. Pillaging is central to a lot of military tactics, though your Builders can repair pillaged improvements without spending a Build action.
While there are major upgrades to both the Trade Route and City State systems, both still feel entirely familiar. Newcomers to the series will not have much trouble getting used to the newly streamlined systems, and veterans will likely find it an intuitive step forward from earlier iterations. The most substantive update to Trade Routes is the new Road system, which relies on trading between cities to create your infrastructure, which are ostensibly supported by trade, rather than from your civ's coffers. Completing a Trade Route will create a Trading Post in the destination city, as well as create an era-appropriate road along the route. The Trading Post will boost your income from Trade Routes in the future, so you'll often find yourself choosing between a sizeable profit and a roadway infrastructure within your borders, since internal trade isn't as lucrative. It's a tough decision, which is the hallmark of a good strategy game.
For your influence over City States, you'll earn Envoys by completing quests and accruing Influence points. City States can be focused on any of the basic game resources, like Science and Production, and you'll get bonuses at 1, 3, and 6 Envoys. If you're the best liked Civ by any given City State, you'll get the Suzerain title, affording even more benefit. For example, while I'm Suzerain of Brussels, I get the unique bonus, "Your cities get +15% Production towards wonders." as well as the universal Suzerain benefits, like getting access to their resources, like Iron, and the option to conscript their military for 20 turns at the cost of some gold. You'll also get vision from the City State, which is far more valuable than I initially guessed.
Research and Civics are still separate, though they're both based on the same system now, where you earn points towards researching new ideas, working your way up the development tree. The next big thing here being the "Boost" mechanic. For each Tech and each Civic, there's a boost condition. The boost for Printing, for example, requires you to build two Universities, rewarding you with 50% of the Science for the tech. This can have a huge impact on your tech order, since you'll find yourself choosing between an advanced tech that's boosted and an earlier tech that's not, and it can be hard to justify Navigation when you can have Tanks in five turns. That said, this is once again introducing new choices that we've not really had before. Without the boost, obviously Modern Era technology will take more time to research, but having to choose between catching up in one area or taking a commanding lead in another where your research is boosted is another seriously challenging decision to make.
Civ VI makes your Faith resource far more valuable than in my previous experience, where it seemed little more than a win condition. Science has always multi-tasked as a win condition and indispensible asset, which the new Faith and Culture system are much more aligned with. With Culture serving as your research points in the Civics Tree, your cultural output is now more essential than ever, drastically altering your Government and Civic options over the course of the game. The different types of Governments are now tied to an arrangement of Policy slots, for Military, Economic, Diplomatic, and Wildcard Policies. Every time you discover a new Policy or Government, you'll have the opportunity to implement that new tech immediately and for free, which helps keep the game feeling dynamic through all of history. In the matter of a dozen turns, you might go from Monarchy to Communism, which comes with two additional Economic Policy slots, which you can use to improve your workers by adding extra builds, making your laborers far more efficient.
Faith is far less give and take, however, as your religion won't force you to replace old benefits, so you're just adding new perks over the course of the game. It's possible to ignore Faith entirely, and I did for my first three games. When I did finally try my hand at it, I had far more fun than I expected. It's worth pointing out that the Religious Victory, which requires you to convert the other civs to your religion, can be particularly challenging to achieve on its own, as converting cities with armies of Apostles is actually far more time consuming than fighting wars with Cavalry. That said, Faith now offers ways to support that endeavor, which I've had trouble with in previous games. The Theocracy government allows you to start buying military units with Faith, and you'll be able to take certain religious qualities that let you build new structures, with options for all of the core resources. You can buy these with Faith throughout the game, so if you've expanded to several cities, you'll be able to kickstart your civ-wide production in a single turn by buying Meeting Houses in each with the Faith points you've been accruing. I'm a crusadey kinda guy, so I just rushed to Theocracy, and insta-built an unstoppable army of religious zealots. It turned into a domination victory pretty quickly.
Civ VI has improved upon nearly every system and mechanic in the game, at no real cost to the experience. It's the easiest Civ to play, but it's also the most complex Civ to date. There's enough default automation that you can ignore a lot of the minutia if you want, but micromanagers like myself will still have all the tedium they can dream of. There's nothing quite as satisfying as pillaging every single tile in an aggressive neighbor's civilization.
Bottom Line: If Civ VI doesn't count as a Great Work, I don't know what should. I'd display it in my Hermitage.
Recommendation: If you hate strategy games, I'm not sure why you're reading this, but you can safely skip Civ VI. Anybody else will likely fall in love.