Koi Mil Gaya (2003)
I managed to catch up with KOI MIL GAYA over New Year and want to give it a thumbs up. I almost turned it off in the first 20 minutes due to some absurd non-science (clue: sound waves are pretty much the one thing guaranteed *not* to make contact with an extra terrestrial civilisation, since they don't travel through a vacuum, and even if they did it would be at something like .001% of the speed of light/radio waves). I think it's better to consider the film a fantasy than science fiction!
However, things quickly started warming up once we moved further in time and Hrithik turned up. His performance as a good natured but mentally retarded adult is very endearing, where it could easily have been offensive. The story is not exactly deep or subtle, but it's plenty engaging and the production values are top notch. Rakesh Roshan definitely knows how to make a slick commercial film. The soundtrack from his brother is good too (note: Hrithik is his son, so it's very much a family enterprise!).
By the way, Hrithik's prominently feature extra digit is not prosthetic - it is a genuine, bona fide piece of his body.