Some people just might not like the first person shooter genre (I'm not a big ファン as it makes me dizzy).
But most people dislike COD in general because it is essentially the same game, different packaging, full price every single time. I played the first few and actually enjoyed them, but then when the franchise really took off from MW2, it really was just near-zero development effort, recycled game code, a new very short campaign while everything else stayed the same for every following release.
Also as a side note which isn't really to do with the game itself but rather the community. COD is known to have the worst online community with literally a bunch of children playing and swearing over their headsets. Few would consider that an enjoyable playing experience.