Imagine how the developers at Bungie felt when faced with the prospect of bringing their decade-long blockbuster series to a conclusion. How can you possibly end a series like Halo?
Apparently, Bungie decided that the best way for its time with Halo to end was to go back to where it began. Immediately prior to Halo: Combat Evolved - as we learned in the manual - the planet of Reach had been the site of one of the largest battles thus far in the Human/Covenant war, and one of humanity's greatest defeats.
Reach casts the player not as the Master Chief, but as an unnamed SPARTAN-III supersoldier whose gender and (armor) appearance are customizable; this is a Spartan who exists primarily as a stand-in for the player. So when the game opens on images of a charred, bombed-out Reach and scrolls down to the sight of a Spartan helmet - the one you just created - lying abandoned in the dust, the meaning is clear: You, soldier, are going to fight this battle - and you will lose.
Your character joins the elite Noble Team as Noble Six, replacing the previous Six (who had heroically died in combat). Right away, this sets a different tone for the game: You may be a Spartan, but you are not Master Chief, gunning down waves of Covenant in a (largely) solo effort. You are part of a team, now - and other than a handful of missions that have you operating solo, you will be working with at least one member of Noble Team at all times.
Players have wanted to go into combat with a squad of the Spartan supersoldiers since the first Halo, and Noble Team strikes a nice balance between the juggernaut-like Chief and the squishy expendable Marines - more than competent enough to help out, but not so overpowered that you can let them clear a room for you.
While Noble Six is as blank a slate as they come, the rest of the team gets to take their helmets off and become actual characters. Their personalities may not have time to grow beyond cliches - the hard-ass tomboy second-in-command, the veteran leader, the friendly sniper, and so on - but they're engaging and likable enough to play their parts. More to the point, the player never sees anything beyond what the team is experiencing - there are no cutaways to scheming villains - which gives the entire campaign a closer, more intimate feel as a team of soldiers realizes they're fighting a losing battle.
Of course, in battle, you're still a Spartan, and that means you still kick a bunch of ass. By Reach, Bungie has all but perfected its famed "thirty seconds of fun" philosophy, and with four Halo games behind them, the developer is able to pick and choose the best parts of each - in that way, Reach feels very much like a "Best Of: Halo" collection. Dual-wielding is gone, but you probably won't miss it as much as you'd think. Your health doesn't fully regenerate on its own anymore, either, which encourages exploration to find precious medkits - and sometimes encourages prudence in engagement rather than blindly rushing in.
And you will have to play it smart. In the absence of the mindless, infectious Flood, your only enemies are the various races of the Covenant as we haven't seen them since the first Halo: brutal and intimidating. The silly little chatter of the Grunts is replaced by incomprehensible alien babble, and they certainly don't seem as much like comic relief when they're charging you with two lit plasma grenades in hand. The Elites charge and flank with deadly efficiency, and the Brutes are just as vicious as they've ever been.