I didn't know which one you were talking about, but the first game is actually not that great imo, and 2 is the peak while 3 was a disappointment, so I'll give the series as a whole an 8.5.
Black Ops 2.
“Anna, my strong, terrifying Anna.” -Cas
"You lack the requisite spine and testicular fortitude to study under me" -Elodin
Video Game GIF Thread