I have both, and i have played like 120 hours of MW2, and about 12 hours of BC2.
I'd say MW2 = BC2.
Going in deteil, i'll like to tell u if u have played COD4 MP, then you will get a hang of MW2 MP very quickly... Very easy to play, you can actually start pwning noobs in the first game itself.. The MP part of MW2 is truely epic, i'll have to rate it in the top 5 mp games i have played, vertainlyl bettering COD4's MP.
BC2 on the other hand, is also an awesome game, has DX 11 if you have a DX card, looks amazing, plays amazing, has uber realistic game physics, like bullets drop in the air if shooted over a long distance, and practically what not. The game is kinda opposite of MW2, the same thing being both games are awesome.
But i'll most definitely say you to get BC2, as it costs 999 for the Limited Edition, and it will be supported way way longer than MW2. Even now MW2 has like no one playing in a low pinged servers if u try to play at 10 midnite, which is my fav time to play. Moreover MW2 costs like 2200 for the PC, as it is not available in India, so i see no reason to get it.
Cheers mate, buy BC2 and remain happy, and buy Black Ops in November
no one gonna play MW2 then