I can't really tell that Crysis is coded badly. Look at what it has to render.....a countryside full of waving vegetation with all that beautiful dynamic lighting / shadows. I haven't seen any other engine attempt to do
that at the same quality - and I'm no expert, but I'm pretty sure the result would be the same if they did. You can build a largely static environment in the editor and get from 40-60 FPS (think COD or similar), so I think the engine is pretty capable, but takes a lot of flack just because nobody else is really trying to push that hard.
I can run this map above 30 FPS with my old 5850....and it makes Skyrim look embarrassing. This engine is 5 years old!
http://www.youtube.com/watch?v=kTuAw_i7ngI
I voted Crysis because it is still certainly capable of bringing a system down.....this map drops me into single digits a lot, but it just looks incredible.
http://earthmachine.home.mchsi.com/crysisfear.jpg
And of course, nobody does jungle like Crysis:
http://earthmachine.home.mchsi.com/crysisfear2.jpg