Black Ops fixed many issues MW2 had and player customization is great, but its currently plagued with its own issues.
The Good: Guns are more balanced as well as perks and killstreaks. The maps are just right and very few don't encourage camping (the exception being Nuketown). The currency system provides incentive to play. Customization galore with emblems, face paint, gun camo, red dot alteration and player tags gives players their own image online. Team killers in hardcore matches are finally addressed. Zombies are back and the world leaders' banter is hilarious.
The Bad: Massive server disconnections, failed transmissions and partying with more than 4 players is impossible to connect to a game (hopefully it will be fixed asap). Too many random games in Nuketown, which so far is the least favorite among the community because it forces players to camp. Nearly every visual aspect of the game is a step back, whether its the grainy look of the environment, the rough gun designs or your soldier's layout, its not impressive graphically.
The sound effects are low quality, nearly every gun sounds the same, important sounds like incoming semtex/frags are non-existent as well as tripping claymores (you hear a faint "click" the moment it goes off). Players names are difficult to see on the same team, which is important for hardcore games.
Many problems this game has can be fixed. Given Treyarch's history of fixing problems, there's a good chance some of these problems will be addressed. However, graphically and sound wise, this game is a step-back.