Been enjoying this game a fair bit, definately worth the 29,90 eur price.
The original Crysis had bored me to tears within the first 30-45 minutes, but Warhead seems a fair bit more action-packed. Some people have been complaining that Warhead is too short, but I am not sure if this is a really valid complaint: I think I am starting to close in to the end of the game and I am at roughly 9-10 hours of playtime so far, if I actually went to properly explore every place I've been to, I would easily add 2-3 hours on top of this.
The game engine seems to have received a slight tune-up in comparison to the original Crysis: I am playing the game on a C2D E6600 2,4 Ghz, 4gb ram, 8800GTS, Win7 system and I am able to achieve very playable framerates at 1680x1050 with some half of the settings at 5/5 and the other half at 4/5. This is obviously without AA, because enabling high amounts of AA will utterly rape any rig except something like i7 920 with a GTX295. However, the game definately does look good:
This is from my rig/settings:
http://jago.pp.fi/images/games/crysis/Warhead0001.jpg
http://jago.pp.fi/images/games/crysis/Warhead0006.jpg
The game also ships with an MP component as well as an editor capable of making full-fledged SP or MP maps. The MP component (called Crysis Wars) is a mixed bag: some of the maps are pretty bland and generally crap, while some other maps are really great fun.