#1 Reason it sucks....
The whole Titan ship makes no sense. The atomic bomb wasn't built and then dropped without testing it out first. How the hell did they know for sure the Titan would create a planet? And if it could, why did they wait so long to build one? They might as well of built a large number planets to play it safe. Also, i read in a post earlier that how could Cale figure out how to get energy but the creators of the Titan couldn't?...just one big stupid plot that almost makes me pissed. Almost.
Plus, the music was horrible. Add the montage, the horrid kissing scene at the end, and the split second that it took to make earth....just stupid as hell.