Black Ops 2 was the perfect mix of a future and modern setting. I gave the game lots of shit before it came out and then when I finally tried it, I ended up loving it and its my 2nd favorite CoD behind MW2.
The maps were great, all the guns were useful (SMR, M8A1, Scorpion EVO, and R870 were my favs), the killstreaks were kickass like MW2's killstreaks, the unlocks were pretty awesome, and the campaign was surprisingly pretty good. Its the last CoD game to deliver a satisfying experience in every mode.
Black Ops 3 just isn't the same.