People like to say how Inception is just a heist movie, and they'd be right; it's a heist movie. Well, sort of. A heist-in-reverse movie. But for some reason they then say that this makes it a "bad" movie.
Why does being a heist movie make it bad? It may have had a basic premise that's been used before, but it was executed well and in a setting that I, at least, haven't seen before. It had an amazing plot and good characters, and I found the whole thing thrilling and exciting.
This movie isn't for everybody, I don't think. The beginning is slow, so if you don't like something that needs a lot of setup before it gets going, then I wouldn't recommend it. But if you find the set-up just as interesting as the action, I'd say, go for it!
The biggest reason why I think people don't like this movie is hype backlash, though. It's not that the beginning is particularly boring, and it's not that the movie is tame, tried, or weak, but when people started hearing about the movie and decided that they were going to see it, after a while the raving reviews built the movie to be something more than what it was. The movie *is* a heist movie, albeit uniquely done, but when people say "It's about going into someone's dreams and planting memories and then crazy stuff happens and then the end is great and it's so good!", it's a brief and succinct summary that doesn't do the movie justice, and at the same time makes the movie out to be something it's not: the movie is about a lot more than just planting memories into someone's head, but the movie also isn't an action-packed thrill ride of insane proportions. It's a lot of things at once, so the only way to be able to tell people who haven't seen the movie about the movie without spoiling it will either leave them disappointed or send them into a movie they may one day look back on and enjoy but was nothing like what they were expecting.
So while I disagree that Inception wasn't a good movie, or a smart movie, or a movie about dreams, and while I do think it is fun and enjoyable, the thing viewers have to remember is that when they go in to see it, put aside all the reviews you've heard and watch it like you have no clue what it's going to be about; you'll find you get more out of it that way.