Very similar to MW2... but that is a good thing.
First, the single player. I have not yet finished the campaign but it is so far very enjoyable. Follow the great COD method of clear area... move on... clear area... build suspense... then add an almost mini game in the middle to change things up a bit. So black ops has been using these mini games frequently. SPOILER at one point you are breaking out of prison and have to use an improvised slingshot to blow up guard towers (from the movie Last Castle for those who haven't seen it). It serves as a great breaker to the still fantastic gunplay. And this may sound a little sadistic but this time around your bullets actually do seeable damage. Which is not a major factor but helps engross you in the combat a bit. When you lob a grenade over enemy's cover and it explodes and you see an arm go flying, you feel like you've actually done damage.
Next, and most importantly, the multiplayer. Again, very similar to MW2 but AGAIN PEOPLE THAT IS NOT A BAD THING. MW2 was one of the greatest shooters of all time so its not bad when something is similar to that. The currency system is a good addition. It allows you to get what you want sooner but doesn't allow you to get everything at once. The customization is really amped up. The levels are a nice balance of close and middle distances with a little bit of large spaces. This is nice because it makes snipers less of an annoyance. And god bless them for not allowing someone to have a grenade launcher and another attachment. Also, with no stopping power possible, it frees up the first perk slot which greatly increases your customization. Now your sniper can have ghost and your other hardline and you don't have to worry about not being able to kill someone.
I have not yet played the zombies mode so I won't BS anyone by pretending. But if it is anything like the zombies in World at War, it will lots of fun.
All in all, a great game. Not much different from MW2 but enough to make it worth the buy. DO NOT KNOCK IT FOR BEING LIKE MW2!!! Nobody knocks Eli Manning for being a good QB just because another Manning came before. But if I must say I would say that game is the Peyton and MW2 is the Eli. For those of you not up to date on football knowledge... that means that Black Ops is better than MW2