the point i'd like to add here is:
Modern Warfare 2 felt finished. It was a quality game, the graphics were great the gameplay was fun and the "limited" amount of enemies per map made it feel like a FPS shooter were we had progressed past being just some grunt to actually being SF.
Black ops is fun yes, but doesn't feel as finished or as glitzy as MW2 did. The Zombie mode is probably the greatest improvement. The graphics are nothing new, the gameplay is the same recycled layout from the other 2 (it works, no need to change it i suppose)
What i didnt like was the levels were enemies kept coming, no matter how many you killed, this coupled with the typically useless AI which gets in the way more than it helps made the game boring on veteran, not challenging, it literally felt like luck of the draw. Sometimes you'd die rushing down a slope, sometimes you wouldn't no real technique to it, which made me get bored and put something else on.
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and as for the "social" side of these games, little 10 year olds screaming down the mic because you have free will and wont do as they say (meaning you mute everyone on your team) doesn't count as a social experience.