One thing I noticed in Titan A.E. was that the computer animation starts out great: thousands of moving objects, textures, wind, ships, exploding planets.
As the movie progresses, the animation gets cheaper. This culminates in the last scenes, on the new and improved planet: the backgrounds look like something done on Bryce with a PC in someone's spare time. Silly geology, cheap fog.
Probably the worse effect is the last spaceship flight, absolutely un-realistic.

I strongly suspect that they run out of render-money (or render-time, the same thing basically).