Picked this game up cheap on Amazon; I was holding off because of performance concerns, but I couldn't pass up $30 for a game I was willing to buy at full price. And I was pleasantly surprised that it runs well with everything maxed out at 1080P on a GTX680. I had my concerns after reading that other people were experiencing performance issues, but I haven't had any yet. I'm using SMAA because I cannot stand the blur that FXAA or TXAA cause; SMAA blurs the image too, but less so (and for some asinine reason all the traditional MSAA modes also apply FXAA, so they're blurry too). But with the latest drivers and patched game, I'm getting performance in the 45-60 FPS range fairly consistently; consistent enough that it never feels choppy or sluggish.
I'm only a couple missions into the game; I'm playing it with the wife and she doesn't typically play action games, but she insisted because she loves pirates. It's great fun, and for once, I actually was grateful to have a built-in tutorial level so she could get the hang of movement. The free-running still has a tendency to cause you to randomly climb trees or narrow doorways, which is a little bit ridiculous in the middle of a chase, but so far I appreciate the addition of more cover areas and the subtle changes in combat. And the water shaders; ooooooh. It looks pretty crappy while you're swimming on the surface, but if you step back and appreciate it from any other angle, it's the best water I've ever seen in a game. And I haven't even gotten to the sailing bits yet (minus the opening chapter, technically). Overall, I'm impressed.