They over-textured it and made the colors less saturated in an attempt to make it look "more realistic", but the animation (that is, the actual movements and acting of the animated characters) was subpar, the models were deforming all over the place, and - save for the shots composed more or less for the trailer - the effects had an awfully cheap and unconvincing look about it.

For example, compare Norton's transformation into the Hulk to Eric Bana's. Bana's, I believed; Norton's, not so much.