At least on Steam, the game debuted to a ‘Mixed’ aggregate rating based on over 2000 user reviews and counting. Most negative reviews complain about the game’s generally wonky performance issues in multiplayer, some frequent crashing, and the obtuse Call of Duty launcher that makes it a hassle to even get into the shooter.
Source: N4G PC CoD 6 debuts to 'Mixed' reactions on Steam: wonky performance, crashes, and the CoD launcher