Okay we've all seen the alpha gameplays. I've never tried the alpha but after some browsing, im seeing people comment that crysis 3 looks and feels the same lot as crysis 2. I'm starting to think crytek is good at their marketing strategy gimmick, "crysis 3 will melt down PCs."
Very likely the final product will look a lot like Crysis 2, with some other features enabled or elaborated upon that will make it more demanding, or they could always go the copout route and incorporate "ubersampling". Either way, this may melt PC's but probably for the wrong reasons.
it will be slightly more demanding by the blurb thats comming from crytec, not a huge amount but it will also be better optomised as the sdk has been upgraded 3 times since crysis 2 came out and crysis 3 will see another upgrade to the sdk... so my guess is you should see 15% more demand on hardware but upto 30% improvement on performance.