Looking at the trailer, personally I think it looks awesome. Nice subtle shading and detail on the environment and enemies that doesn't detract from the overall simplicity, and then you get to light up the whole screen with massive firepower when you start shooting with one of the big weapons. What do you think looks bad about it?
(Not a rhetorical question. I'm not a graphic artist. I'm curious if I am missing something that a professional would spot.)
If it's not immediately obvious to you, then I can't explain it either, or at least I can't be bothered to try. Some people don't see it. It has nothing to do with being a graphic artist. It's not about technicals, it's not something that comes off a checklist.
(Not a rhetorical question. I'm not a graphic artist. I'm curious if I am missing something that a professional would spot.)