It's not bad...but it's not really all that good...
When a company begins pumping out sequels, we expect improvements and a great deal of new content. The first two Modern Warfare games were top-notch kill fest, full of action, some suspense, and amazing multiplayer. Treyarch and Infinity Ward run the Call of Duty franchise, and the latter, in my opinion, is the best at it. Treyarch saw the success of it's brother-in-law and decided to copy him to the letter. Using a good formula is great and all, but pumping out the same game every couple of months leads only to one thing: Stagnation.
A few new toys in multiplayer, a little extra customization and a new (if mediocre) campaign is all that you'll get with Black Ops. In conclusion, the game is not terrible, it is just another Modern Warfare. If you want a new, very fun modern combat simulation, but don't feel like buying the same game, go and buy Medal of Honor.