Originally I was skeptical of Black Ops 2. I heard there were a TON of glitches with Black Ops 1 (especially multiplayer) so I avoided it entirely. And I was prepared to do that for Black Ops 2... But then they announced they were moving towards a futuristic setting. Which has caught my attention and made me rethink staying away. I won't be getting this game at launch, but I'll be interested in seeing how it does regardless.
I'm a bit of the opposite opinion regarding this shift towards the future...
They're rather running out of things they can do in the past. They've covered World War 2 a lot and Vietnam war. So it's getting time for them to stop looking at the past and move forward.
Though they aren't making this game set in 26th century so there really is no comparison with Halo to be made. This game is set on 2025 (which is only ~13 years off from now if you think about it) and will feature tech that is very likely what we're working on now in the real world. (We have thermal cameras already so it's not too much of a stretch to improve that and combine it with a sniper rifle for shooting through walls.)
Plus Halo and Call of Duty have slightly different play styles (CoD is a bit slower, take fewer bullets to die, can't jump as high/far and have different weapons). The points they do share are: futuristic setting and they're first person shooters.
Plus making a game set in the not so distant future allows them to get creative with weapons while still using guns that we're familiar with.
alm: leave the futuristic stuff to Bungie.