I've said it before, but I enjoyed it enough but will never forgive it for introducing the future shit into the series.
The original idea of Mason being on the run from the CIA searching for an alive Reznov, if true at least (and based on all the computer stuff in BO1 seems like it) sounds like it would have been much more interesting.
I feel Black Ops II was the start of mediocrity that plagued the CoD series up until recently.
Don't get me wrong, it was a fun time with multiplayer and campaign. The Pick 10 system was a much needed change for class loadout customization. The maps were distinct enough to be standouts. Hell, they even "fixed" sniping from Black Ops 1. It does reward you through progression with extended weapon usage.
I was largely uninterested with the campaign compared to Modern Warfare 3. I liked the concept of going back and forth with past and future. I had more fun with the past segments than the future; it felt like an extension of Black Ops. Strike Force missions were just multiplayer maps of infinitely spawning enemies.
Best way to describe Black Ops II is throwing everything on the wall and hoping it sticks. The futurist twist, while not bad compared to Black Ops III, felt cliche. I couldn't remember what happened once it all ended. They tried to turn Zombies into an "adventure" mode with TranZit. The execution was horrible. You have to rely on the bus to take you all over the map. There's too many dead spots with that bus mechanic. And don't even get me started on the aesthetic and Easter egg.
You had to buy DLC to get the most out of Zombies. Even so, they relied on players doing complex Easter eggs to fully experience those maps. Not everybody has the time or skill to party up and do outrageous tasks to further your bullshit lore.
DLC, there was a LOT of it with Black Ops II. Weapon camos, calling cards, even extra class slots. In retrospect, it's not as bad compared to what would come afterwards. I'm referring to them adding loot boxes, purchasable currency, P2W weaponry. But, I will argue that Black Ops II started the microtransactions trend that plagued Call of Duty.
Overall, Black Ops II was overrated in my personal experience. Modern Warfare 3 was better.