The single player campaign might be shorter than you'd like, but 15 levels isn't too bad for a game today and the levels are good, decent lengths and there is some variations to keep it from getting to repetitive e.g. using vehicles and changing from stealth to all out attack. The gameplay (which is the most important thing in a game) is very good, the graphics are great, there are lots of weapons too.
It's a shame it doesn't have a Spec Ops mode like Modern Warfare 2, but it does have the Zombies mode, which seems like a good inclusion and the mini arcade game too 'Dead Ops Arcade'. Despite the fact that it can really annoy you the multiplayer is great with achievements to obtain and lots of different modes on Xbox Live. I've not really lots of good features new and old like earning currency to buy certain items and things like killstreak rewards. It can be annoying when the odd time games suffer from lag or lose connection, but most of the time it plays great and there's hours upon hours to play with the challenges and Prestige modes included to have something to strive for. The new maps are great (hopefully at least one more map pack will be out soon.) aswell as the default ones, though some come up far too often and others seem never to anymore (Summit compared to Nuketown springs to mind.)
Overall this is a very good game both off and online and despite some issues and the fact that it can really annoy you it's quite addictive and very fun to play most of the time. The price was too much when it came out, but now that it's gone under £30 I highly recommend it.