I'm not sure I see what you mean; in the trailer they added a slight darkening/depth of field blur to the corners of the screen. The lighting overall is a little darker. Otherwise, it looks basically the same, except the models look a bit worse because they're not textured enough; Ryu and Chun give off the kind of smoothness/shininess of a plastic toy, similar to the way KoF characters look now. I prefer the more organic "clay" look in comparison.

The problem with teeth on some of the characters seems to arise from the fact that they didn't go anime style. In SFIV, and in anime, everybody's teeth are essentially just a big block of white. Much like male nipples, lips, and women's noses, anime artists hate drawing teeth in detail because it's kind of an ugly/inconvenient part of our anatomy in a way.

In SFV people actually have real teeth with distinct separations between each tooth, they clearly have gums, etc. As the camera moves away from a smile, these distinctions combined with lighting/shading can make the teeth get visually a bit messy. And in the right pose, a bit ugly. I think Ken's teeth could use some bleach in his character select pose. However overall I think it works fine.