Gamasutra gives us a look at the making of Crysis Warhead. They talk with Bernd Diemer, a designer at Crytek Budapest. He talks about the reasoning behind the game's unusual format, the tricky balance between player guidance and player freedom, the maddening intricacies of NPC AI, and the problems with the often-maligned drastic shift in gameplay towards the end of the original Crysis.
On concerns that the action focus could detract from the sandbox feel: From the pacing side, we decided not to have gameplay-specific levels like we did in Crysis, where we had, for example, an entire tank level and we tailored the entire level to have the most preferred experience being in a tank.
In Crysis, we had a bit of an old-school mentality to level design: "Now, it's the vehicle level." In Warhead, we have shorter sections within levels -- you don't have one level with driving all the time. There would be a short vehicle section, an infantry section, maybe another vehicle section, then some aliens, then some North Koreans.