The general overuse of cgi? It's a comic book movie set in a fictional city following people with superhuman abilities. It needs a lot of cgi because of the type of film it is.

Character models are tricky to seamlessly get right. The same was as Wonder Woman jumping out of the trench in WW or Iron Man without the head looked slightly unnatural. It's usually evident when the character isn't wearing a full body suit. So in Civil War every character who had a full suit was doing crazy shit in the air, because it was easier. The people with their faces showing stuck to small scale stunts on the ground. It's going to take a bit longer to get Wonder Woman, Cyborg and Aquaman right in this film because of that.

I don't see how slow motion effects diminish the look of the trailer. Hell guardians had tonnes of it and it looked great. And the physics of explosions, landings, flight etc is still being worked on. They haven't even finished all the footage they need yet. Never mind perfected the cgi.

Three months from now it will look a lot better, but for now I think it looks great.