Check out the latest Steam reviews, mentions of bad performance are actually fairly rare. Apparently, for some people, framerate dips still happen, but aren't nearly as severe. The game ran okay for me on launch and runs perfectly now so not much to complain about.
As it always is with these things tho: YMMV
More or less fixed for Nvidia cards I would say. They really should have waited, they must have known how dire things were.