There are spoilers here.
There have been tons of negative reviews about Portal 2. When it was first released, there was the controversy over the add-ons Valve made available for purchase. This content was nothing more then hats, gestures, and the like. It's nothing that makes the game better. There was also problems with how long the game was. I've beaten it three times now and I can tell you it's certainly not just two or three hours long.
Having said that, there are even more reviews of Portal 2 that complain about everything from "it's a puzzle game" (duh..) to the test chambers. Here's one review that talks about the price, among other things.
First they call it "witty" and "comical." Yep, I agree. But then they say they would have given it five stars, not two if it was $20.00 on Steam. Apparently because there are games like Call of Duty, Killzone 3, and Dragon Age 2 out there, Portal 2 should be cheaper. CoD is known for its short single player campaign. There's multiplayer too, but the single player only lasts about five hours. Besides, it's a FPS about war, how is it similar to Portal? Dragon Age is an RPG. They can last forever. I'm fairly certain there's no Portal gun or companion cubes in Dragon Age. It's useless to compare Portal to games that are the same price but in completely different genres.
Looking at the other points of the review:
The part about the environments not changing is untrue. If you look at the three main sections of the game (waking up GLaDOS, old Aperture, and Wheatley's Aperture) they are vastly different. In the first game, the environments didn't change much. That can not be said for Portal 2.
And of course, the story has no twists and turns... I mean I always thought that GLaDOS was going to turn into potato one of these days. Or that Wheatley was going to be a "bad guy." Or that you could make portals on the moon.......
But if you're a fan of Valve, none of this matters cause we're mindless fanatics. Hooray for insulting people who liked the game too. Good job.