Ascension going free is nice but you're going to want the expansions at some point. It's fully featured without them though. The expansions have been on sale in the past.
Ascension and Reiner Knizia's Samurai are the two best async multiplayer games on Iphone. Lost Cities in third place.
Battleline might have been a contender had it had a better implementation. It is a better game than Lost Cities in most ways but LC's app is better designed, prettier, and sexier.
Don't get me wrong, Ascension is far from the best card game you'll ever play but Playdek's masterful app design and the game's perfect balance of depth and turn brevity means it is easy to get into or come back to on down the line. Many others like Nightfall and Summoner Wars are denser and more obtuse.
Really, in a general sense, I use Boardgamegeeks for my Iphone gaming news more than anything else. "Traditional" games have been a wasteland on Iphone with few exceptions. But board and card games vs. AI or online have been some of the most consistent fun I've had. And I don't mean your dice throwing monopoly crap. Real games of skill and chance like Battleline, Catan, other Eurogames, etc.
It was a smooth ride.