I got the game today
Finished the single player missions now. It took me about 2 hours on regular difficulty (i kept dying in some of the levels). The "less than 1 hour of single player content" is definitelly not something that will apply to everyone. Then there is all the trophies, time trial and Hostile mode left as well. Personally i think i'll get at least 5 hours out of the single player content since i will try to get as many trophies as possible.
I tried 4-5 rounds of multiplayer so far. It feels pretty smooth indeed. The guns and controls feels fine i think. It might not be the 100% console/PC Call of Duty feeling, but it is not far from it in my opinion.
I got to try 8 player free-for-all on Nukehouse. That was non stop action hehe.
I dont understand one of the previous reviews who claimed that this game was a big middle finger to the COD fans. The same with the comment about "after you've played a few rounds online you realize that this purchase was a mistake". I'm a COD fan and i dont feel this way at all. I realize that the guy is speaking his opinion, that is fine, but he also seems to say that it will apply to most people. I dont agree with that personally. If someone expects a 1:1 PC/console COD game on Vita, i could see some disappointment, but i think it is important to keep in mind that the Vita is not as powerful as the PS3.
Overall i think that Black Ops Declassified is a pretty good first attempt, especially concidering the short developement cycle.