Many people tend to forget that Warhead is an expansion and as such, it offers too little to deserve its high marks!
Well, they missed nothing as there is nothing to miss here. I loved the original Crysis, even though I could barely run it on my machine, but now I get exactly the same game, only much shorter. Arsenal additions are insignificant and you will rely entirely on old weaponry. Enemies are the same. I noticed that now there are giant squids that drop bombs, small squids that shield other small squids and North Koreans with nanosuits, but that just can't pass as new additions. The levels are pretty much the same and even the events are the same, only the perspective is different.
What is more, even though Warhead is a stand-alone expansion, its part of the story is so incoherent, that you must have played Crysis to know what is going on.
I finished Warhead in five hours on hard my first time through the game. This is too short even for an expansion pack. There are no linear levels this time, but that doesn't mean that there are more sandbox levels.
Speaking of levels, there are still some great designs as the train level and the whole jungle in general is represented magnificently. In fact the only boring level is the mine.
In my opinion, there is only one thing in this game that makes it deserve more than 7 and that is what everyone expects from Crysis - graphics! No way to disappoint here! Warhead looks even better than Crysis and as I already said, the whole jungle is represented somehow better. Day-night cycle, weather effects like snow and tropical storms, everything just looked to me more impressive this time. I also noticed a nice blur effect when turning fast, that I can't recall in the previous game or maybe it just didn't look that good to leave an impression.
However, it is not entirely true that Warhead runs better than Crysis. While there is a slight improvement in frame rate on most levels (not enough to be of significance on high-end machines), the frozen levels run even worse than before, especially the first one. Once again, I was playing alright with everything set to "gamer" but I had to reduce all to "mainstream" on the first frozen level and it was still barely playable - I had to lure enemies in tighter locations in order to get an FPS boost and be actually able to aim.
AI seems to have been improved though. It is most notable with the aliens, who can actually kill you now. I was also very impressed with North Koreans who seem to have memory, flank and use cover. I was very impressed once when I got pinned down behind a rock. I switched to cloak mode and slipped away, flanked the enemy and observed - they were still looking at that same rock where I stood moments ago. One group used covering fire in its direction while another one moved on the side, flanking. They even hurled a grenade behind the rock.
Another time when I really liked it how the game is not cheating but actually calculating was when I was sitting tight in some dense bushes, not using cloak. There were enemies just three steps away from me, looking my way but they couldn't see me through the foliage until they literally stepped on me in the end.
Of course, it doesn't always play that smooth and enemies tend to get stuck to walls from time to time or react inadequately to a certain situation, but in general, AI in Warhead is brilliant.
I can't think of anything to say about sounds and music, good or bad.
I had no chance to test multiplayer either, but I hear it is nothing that special.
Overall, Warhead is the same tense action game as Crysis and if you liked the firefights there (there is no reasons why you didn't), you will like this one as well. However, it offers too little content even for 30 bucks.