It does have that endless hostiles mode, but yeah, the focus is on the multiplayer. The back of the box barely mentions anything single player, in fact.
But BLOPS Declassified is...good!?

Much better than Resistance was. It's the best portable FPS I've ever played.
Too bad that is really not saying much. The game is scaled-down and uses smaller maps, but that makes the eight player matches not feel so empty and the game really feels like Call Of Duty despite its flaws.
The controls are pretty well done; I had to turn the sensitivity way down and turned off the auto-run and was able to jump right in. A lot of players really, REALLY suck online and I think it has to do with the auto-run and aiming settings. If you don't adjust them, you aim all over the place.
Encountered one odd glitch (unless it was cheating somehow) where everyone on my team would respawn, immediately die, and respawn again. It kept saying that a single player on the other team was killing everyone.

But at least I was able to keep on playing-- BLOPS II already locked up my 360 once.