Back to the basics! From the first Crysis, which was supposed to be the best looking game with insane physics to the last one, which is... good looking?
First crysis had a great story, great enemies and memorable landscape. Making your way through the jungle or using the editor for fun makes this game a great time killer.
Crysis 2? Mmmmmh I was never too fond of it, it lost many of the good aspects from Crysis 1 and the story is forgettable. It's still nice to have it as a bonus :)
Crysis 3 is great, good looking, forgot some of the mechanisms yes, but brought upgradability and new capabilities to your exo skeleton, alongside with a great story, immersion and enemies. The online is still active but it will never be as good as the first one unfortunately!
Those three games are classics now and should be played by anyone who didn't try them out yet ! :)