As long as there has been science fiction, there have been amateur physicists who trash movies because they "defy the laws of physics". Get over yourselves. This is fiction and it is o.k. to break a few laws so long as the plot doesn't hinge on the theroetical inaccuracies. I liked the first 95% of the movie...I thought the visuals were well done, I liked Pitt's character, and thought it had a Bladerunner/2001 Odyssey vibe going. Then the ending...well....it stunk.
**SPOILERS***
O.K., so Pitt's charater has a bad relationship with Liv Tyler and it apperared his father went crazy in Neptune orbit. So when he reaches his father's ship, we find....his dad is crazy and when he gets home, he tries focus more on his relationship with Tyler. What a waste! No suprises, no clever plot twists, no insight into the human condition. They just played out the narrative we already knew. If discovering you have daddy issues and you need to learn to "love the one you're with" is what passes for character development, then we need to go back and learn what makes science fiction good.
I'd recommend watching the movie up to the part where he finds his father's ship - then leave the theater, go home, and make up your own ending.