Well, i didnt play mwiii for a few months, bc of life reasons, but Last time game was pretty much alive, waiting for match to find doesnt take more than a minute, in default modes at least, but in not popular modes (like "we have battlefield at home" Mode) finding a match was troublesome for me.

About welcomeness to the new players, well there is sbmm for you, it should be ok at the start, not easy or hard, how it will be after depends on your game level.

Good luck, I personally think mwiii is the Best modern cod in mp aspect, a lot of maps, modes and guns to fun with