Its very playable on high end rigs right now.Worse. At least Crysis was playable on high settings with high-end PC's. This isn't. At the minute.
On my mid end rig Q9450 + GTX260-216 @ 1920x1080 I get a constant 30FPS with no slowdowns and max details except for medium texture quality. If you don't have some kind of quad core I would say forget it but not going to slate R* for this as they recommend you use a quad & the console versions were designed on 3 cores plus so if anything its good of them to make it run at all on a dual core or lower but obviously you will have to lose details to get a playable FPS or just run it at a console 720P resolution in a window. They could have made it quad core only but then people would have moaned why no dual core support so R* cannot win either way!!