I saw this last night. It was definitely worth six dollars.
I know a lot of people have been complaining about the movie (long before any of them saw it) because it's not "faithful" to Asimov's work. Not having read much Asimov, I can't comment, but I can say that based purely on its own merits, the movie is good. Excellent CGI work, good writing, and lots of satisfying action. It's one of the better sci-fi movies of late.
Like Troy, this movie may get hammered by critics and bookworms alike because of its departure from its origins, but pretty much everyone else will appreciate it for what it is: fun.