Everyone should play this game. It doesn't matter if you don't like platformers; it doesn't even matter if you don't like games in general. When someone says that games are all generic and boring, it is because they have not played this one. When someone claims that games are all juvenile, are all centered around violence and machismo, and cannot be considered on the same level as other media such as books and film, it is because they haven't played games like this.
Everyone should play this game, because it is utterly unique. I can guarantee you've never played anything like it before, and likely will not again. Players may think, when they start the game, that it is a 3D platformer, similar to many games on consoles recently, but they will soon realize that this game is so much more. You can't talk about this game in terms of genres. It may use some ideas common to certain game genres, but what it does with them transcends simple categorization. I think that for people who do not believe that games can be art, Psychonauts is a perfect rebuttal. Not only is it incredibly imaginative, but it utilizes different visual styles and even gameplay styles to reinforce its themes brilliantly. It is an ideal example of what can only be accomplished in games.
In the strictest sense, Psychonauts is not perfect. But its imperfections do not matter. They are small, trivial things, the types of things that reviewers find because they don't want to write a review that has no criticism at all. Even with a few frustrating parts, even if some things could have been a little more streamlined, everyone should play this game. Because it's what it forms as a whole that matters. Because it is, at its core, genius.
Also it's hilarious.