Both the first Crysis and Crysis Warhead are both available for 9 bucks (well, $8.99 technically but I'm rounding it off..
), a good deal IMHO. However, even with the latest i7 Processor and latest video card they still struggle a bit to run on current rigs so for anyone interested in picking up both games I'd suggest going here to do some "tweaking":
http://www.tweakguides.com/Crysis_1.html
I used this guide to help get Crysis Warhead to run smoothly. IMO Crysis Warhead isn't quite as god as Crysis 2 & 3 but it's still good solid fun. Hell, I think it's actually better than the first Crysis. And for those that haven't picked up Crysis 2, it's also available for roughly 9 Bucks on steam so I'd recommend picking it up as well.