This is mostly due to the use of some low-resolution textures. You can see very far into the horizon, with very little fogging. There are no popup or polygon glitches to be found. Spell effects are very well done, and a few are certified jaw droppers. Just wait until you cast Summon Elemental for the first time.
Animation ranges from good to absolutely pitiful.
For example, one level features a dog that you must follow. Doing so will be painful, since the dog appears to have exactly two frames of animation. It will hurt your eyes. The frame-rate does dip at times, but never slow enough to give you serious problems. Sure it's not the smoothest moving game, but it's not too bad either.