Snyder could have made the ending just as grotesque even with the Manhattan bombs. I would agree that that was a failure on his part.
To clarify I'm not saying that the idea to use Manhattan's energy devices instead of the Squid was a bad idea, just that Snyder should have included the carnage in the streets of NYC when doing this. All in all I like the movie...it does bother me that there are stupid little things here and there that keep it from being great.
Agreed. The grotesque horror that was present in the comic did not carry over to the film, and it didn't' have to be that way just because he changed the ending.