GTA5 played fine on Xbox360 and PS3 so I'm certain it will be playable even on somewhat dated gaming PCs, for the true 'next gen' experience you will need some serious hardware though I think, especially a lot of fast RAM and of course high end graphics card.
I'm preloading GTA5 now and looking forward to playing whenever it's made available to me, launched on 14th but not sure what time zone that's in.
I'll be running it on a 2600k i7, 970 GTX, and 16gb RAM so I think it will run medium setting very well and the high or 'ultra' settings will run but will chug the frame rate down at times.