I do want to say that I think people need to go into the movie with the right expectations. I do not consider this movie to be primarily a philosophical movie - while it deals with some philosophy elements, I much prefer to think of it as a psychological action thriller. It has a really cool plot, a clever and mostly-believable mythology, some great acting, and a few really cool characters. Many of the critiques I've seen are that the philosophy isn't all that great - and as long as you're not expecting it to be then it won't be a problem.
Is the movie perfect? Not at all. There are a few major plot holes and occasionally characters act kinda dumb. There's too much gun-fighting that feels out of place and unneeded. Perhaps most annoying, at least to those of us who notice, for a movie so obsessed with timing there are cases where it falls into the stereotypical "let's have 10 seconds take 60 seconds of screen time" thing that irks me.
All that said, I was enthralled throughout the entire movie. While not earth-shattering philosophy, it does engage your mind throughout and feels much more interactive than most movies just because of how twisted and deep the mythology is. It's a sci-fi movie that isn't entirely believable, but it just doesn't matter - it's pretty to look at, has a great plot, and is beautifully executed.
Also, I have to say, I have tremendous respect for Leonardo DiCaprio, who turned himself from teen pop idol doing bad movies to a consistently excellent actor in his adult years. Ellen Page is also one of my favorite young actors of today and she does a fine job in this movie as well, as does the rest of the cast.
This might sound like a very vague review that says almost nothing about the movie, and that's very intentional - I don't want to give anything away. I managed to walk into the movie knowing almost nothing about the plot (a feat I also pulled off with The Matrix) and I'm much happier for it. So, if you like cerebral action movies, or Christopher Nolan, or really just movies in general, go see it. Go into it expecting a fun, intriguing story that isn't a dissertation on existentialism and I think you'll really enjoy it.