No but it probably will be. The inherent violence of the game (shooting things) is almost enough by itself. The ESRB has a precedent now of making shooters rated M. Most shooter nowadays don't even have that much gore or language or anything like that really but are still labeled as M. Rating a shooter M is a safety net for the ESRB and game developers to avoid potential issues of inappropriate content. If they rate the game M, it means that anyone under 17 who plays the game is subject to their household's censorship, not the ESRB/Gaming Industry's. Also rating a game M isn't going to effect sales enough to not have that safety net.