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Crysis pushes your GPU more than other games do. It's the same for everyone. Hence, temperatures are higher than when playing other games.
Besides that, Crysis is a very demanding game and still brings the most powerful current systems to their knees.
100C is very hot, but I reached those temperatures in Crysis with my old 8800GTs sometimes, too. You could try to clean your card with a can of compressed air to get rid of dust inside of it, or you could also reapply some thermal paste on the chip itself.