The last example actually demonstrates that this is not an absolute system of categorization. Sometimes puzzles are meant to be puzzles, because the setting requires a puzzle. But the difference that integration makes to how a game feels is apparent even in games that are all about puzzles: Take Riven as an example. A lot of games have tried to ape Riven, but most have failed, including some of that game's sequels. Why could Riven create such enthusiasm in so many players when other games, with equally devious puzzles and equally pretty graphics, could not? A significant part of the answer to that question might be in the puzzles. The Age of Riven is full of mechanical artifacts that the player has to understand and/or repair - but what the Age of Riven is not is an excuse for putting together a bunch of puzzles. Riven is a place, and the artifacts are an essential part of that place, a natural outgrowth of the civilization that inhabits it.
Perhaps this is being unfair to puzzle-based adventure games. After all, aren't puzzles what the players want? Why blame a game for delivering what its audience desires? But then why string these puzzles together in the form of a narrative? Because Myst did it? Because Riven did it? Or is it perhaps because somewhere deep down most of us do want a story? Either way, if the world and the puzzles are not tied together, they will eventually fall apart. Not everyone minds this, but I'll be bold enough to claim that most people do.
Let's leave puzzle-centric games alone and think about games in general. Again and again, game designers feel the need to break up regular gameplay with puzzles of one sort or another. Here the distinction between puzzles and obstacles becomes supremely important. If the gameplay so far has been good and the player is immersed, a puzzle can very quickly damage that immersion and take the player from experiencing a world to just playing a game. If the gameplay has been mediocre, the frustration can be enough to make a player quit. And if the gameplay has been bad enough to make the puzzle more interesting than the rest of the game ... well, in that case the game designers have more serious issues to worry about.
But what if the truly immersed player encounters an obstacle and not a puzzle? If he or she is really experiencing art at its most successful, that is art that has temporally become reality, then encountering an obstacle will simply confirm and strengthen that reality. And if the player is only semi-immersed, a well-conceived obstacle may be enough to transform an enjoyable experience into a memorable one. An obstacle turns a level into a place, a game into the chance to interact with another world. It allows us to use our problem-solving skills in the support of narrative, and so we become part of the narrative. Puzzles throw us out of the story - obstacles pull us in.
Context, in art as in life, is everything.
Jonas Kyratzes is a writer, director and independent game designer. When he's not working, he plots with a small black feline and rides the solar wind. He also has a website, but it smells of mushrooms.