It's actually movie quality. The characters are authentic. Everything just comes together so nicely. I almost wish this was a movie and not a game.
And that is precisely the least impressive part about it. It will probably be a perfectly decent game, all told, but that's because there's a good sense of what GTA is about and how it plays. If this were new IP, I'd be extremely dubious. Games are not movies and this obsession that some of them have with being movies is not a good thing.
That said, a trailer isn't a game either, and it's not clear to me whether a trailer should emphasize the gameplay or the cinematic aspects of a game like this. Again, it's not like people don't generally know what GTA is about. Arguably there's very little point in highlighting gameplay, and since the cutscenes are in-engine that's a plus.