Admittedly, the first trailer for Gangster Squad has a lot of ground to cover. With half a dozen major roles and an extensive supporting cast of prominent acting names, there are a lot of people to introduce. So if not all of the characters seem especially fleshed out, you can't really take issue with the movie to come. At least not yet.
That said, Gangster Squad doesn't seem to really offer a challenge to any of its major players. The world has seen what Sean Penn can do; as one of the most celebrated and trusted actors in Hollywood, it's difficult to really get a surprise performance out of him. Expectations are consistently high. But if Mickey Cohen is as flat a role as he looks to be in this trailer (which, honestly, he probably isn't), than Penn's inclusion in the movie would be sort of a waste.
The same looks to be true for the characters played by Josh Brolin, Ryan Gosling and Nick Nolte: will this movie limit them to stone-faced exposition, half-assed suave-itude, and gravel-voicery (respectively)? Or can viewers believe that this trailer is misleadingly simplistic, and that each of these fine actors will not only live up to, but possibly exceed expectation from past performances?
Until the next piece of footage comes out, it's hard to know for sure whether this will just be a well-cast but unsubstantial crime drama banking on likable faces, gunshots and ostensibly tense scenarios, or something legitimately interesting. Either way, we've got a sort of Crazy, Stupid, Love 2 thing going on between Gosling and Emma Stone, so you can mark that in the Pros section.