Admittedly, I have only played Multiplayer; I'm Level 53 no prestige yet. I play on PC wherein I get a ton of lag. MP is too addicting for me to care about any other mode, though I attempted to graze Zombies only to be met with worselag than on MP.
So, my first impressions have basically been these: the game is a ton of fun, the customizability is a dual edged sword*, there are some five or six maps that I like but cannot enjoy because of PC lag, Nuketown once again is the greatest map to ever exist, my favorite modes are Hardpoint and Domination.
*My biggest problem with the customizability is that you only have 10 things to choose from, and certain things take up points when, IMO, they should not have. So, if I pick "Perk 1 Greed", that uses up one slot. But when I go to pick my second tier 1 perk like P1G allows me to, that second perk also uses up another slot! I know, it's for balancing issues somewhat, but it just feels a bit...claustrophobic?