Some of the mechanics stay the same(60fps, the game engine), but they add new perks, guns, attachments, playlists, maps, etc. Every COD game plays completely different than the last. It's not the exact same game, it's just a similar game at the core, put into a completely different settings. If it was the exact same game, than map remakes would play the exact same as they did in previous games, but that is never the case. Just look at all the remakes in BO2, and then tell me those maps play the exact same as they did in BO1. You can't, cause there's so much stuff that has changed since then, that you have to play the game differently.
As for this game, it play completely different than any COD I've played. It's one of the slowest/campiest FPS I have ever played. Since the health is extremely low, you have to play the regular playlists like hardcore. I just stick to domination or crank, cause those seem to be the only playlists where people are actually moving around. Playing regular Team Deathmatch or K/C, and all I see are people camping in corners or holding down hallways or certain parts of the map.