I don't think that was obvious at all. I was wracking my brain trying to think of who it would be.
(SPOILER)Since Ben's out to get Penny now, I imagine that Desmond will have some screen time as well since he's her man and all.
All in all I thought it was an enjoyable finale. I do like the fact that they tied up several lose ends and only left a couple of big ones open. (SPOILER)The fight scene between Sayid and the lead mercenary guy was surprisingly well choreographed. It's too bad Sayid didn't get another chance to flex his thighs of awesomeness, though.