There are a regular group of a couple of thousand people who are always on there. I play a fair bit too. It's a great version.

I haven't played it in a long time. Shortly after Ghosts came out. 

I do from time to time.

Usually 1500-2k people online compared to titanfalls 5k its not bad.

People still play CoD4 on PS3 so I would say that people do still play it.

I'm sure there are. People still play the original Gears of War to this day, so a game from 2012 is gonna be still played online.

I still play Ghosts
I never see more than 500 people on at once, but its still a very minimal wait time.
I play better on the game pad. I feel the small screen makes it easier to see.

I dont think ive ever seen it under 600. Usually when im on its the mid 700's

It has dual screen local and is worth the buy for that alone. Try sniping on the TV with the heavy machine gun laying on the couch facing away from the TV on the gamepad. A brilliant yet unadvertised Wii U exclusive feature. 

The Wii U has great online. Even mass effect 3 always has people online. The bonus is less creepers and annoying people than I experienced on ps3. Im writing this on the gamepad and might pop black ops 2 in now.

I have friends who are on it regularly.  They are good people so if you are looking for multiplayer action I would say go for it.  Otherwise, have you considered Mass Effect 3? 

Mass Effect 3 definitely has the best horde mode on Wii U in my opinion. Just lacks the last 2 multiplayer DLC packs and challenges the other versions got. Never have problems finding Bronze and Silver matches.