I love movies based on scientific themes or adventures. Such movies are also useful to maintain scientific as well as rationalist spirit in society.
What about it?
My favorite sci-fi is I, Robot.
My favorite sci-fi film is WALL-E. {Obvious choice.}
Good choice, man!
And welcome to the forums. 
Not including Wall-E i’m going to say the 1977 Star Wars.
WALL-E has a very good story and message going on (this is coming from me after I did the commentary on the film), but after watching many awesome movies in my life, I still have to say that it did not impact me as much as other great films.
The science-fiction genre, AKA the sci-fi genre, was actually not one of my favorite in the past (but that was never really the reason for me not going nuts over WALL-E; I never saw WALL-E as under the sci-fi genre when I first watched the preview trailer). I always thought it just composes of aliens, spaceships, and boring, geeky trivias no normal movie-goer would really remember. Obviously, I gained those impressions from Star Trek; a reason why I am not watching that, even though it is going to be directed by a kick-butt director (whom directed Cloverfield, I think…).
Then there was Men In Black. Will Smith blew me away. I really love Will Smith’s acting, so if you mix that with aliens, superb CGI effects, big guns, and a freaking awesome story line written by the same guy who had brought you the '90s Batman and Batman Returns, boom. Lots of cash, lots of fans, a grand franchise, and you wouldn’t even remember that it was based off… something. I think it was a comic-book or a game, but I am not sure. 
However, that is just how I got into liking the sci-fi genre. No, the real gem in science fiction movies was actually made at a much longer time ago, unfortunately. It is just another example of how movies are degrading in quality as time moves on, but as I said in the commentary, it is understandable. As ideas are taken up, stories become less original.
Anyway, the gem: the Alien series. 
No, not the 3 and the Resurrection. Those are just pure humiliations. 3 was interesting, though, and Resurrection had a lot of action; but both were no Oscar materials, like Alien, and most definitely the better sequel, Aliens.
God, those are amazing, in terms of the story lines, the SFX of that time, and the amount of gore and thrills, and this is coming from a guy who doesn’t like aliens, and this is also coming from many strict movie critics. Filmmakers today, those making movies under the sci-fi genre, especially, should pick up a thing or two from these two movies. I mean, they have a sequel that actually does not suck. How about that?
But of course, WALL-E was very close to that. Sure, its lack of maturity might get some cynics talking, but still, it has a great story, and it was quite enjoyable, too - as a Pixar feature. As a summer blockbuster hit, Alien and definitely Aliens score much better as good movies.
Ah, sci-fi. Used to be one of my favourite move genres, and I loved watching the cheesy ones in particular, such as Armageddon and [/i]Mission to Mars[/i], I think it was called. All those apocalyptic, ‘some massive meteor is going to collide with Earth in 9 hours and 45 minutes!’ type films. Alien is brilliant too, especially the original. A more recent sci-fi film that I enjoyed was Sunshine, and the horror elements it had made it even more of a rounded, generally good fun film to watch.