I bought Warhawk.
It was great for a while.
Then I realised the bandwidth it used wasn't worth it.
I wouldn't buy a multiplayer-only game now because, quite simply, I can't be bothered playing online enough to keep my skills up. If it's a game which has multiplayer I can pick up occasionally, then I'll be encouraged by the multiplayer being good, but it won't sell a game to me these days.
Although I do intend to play MAG at some point. I've seen it played literally twice, and it seemed fun. But I wouldn't be playing often enough to be worth buying it.