I'm most excited to see that there are a lot of different engines. More competition and more variation sounds great. All too often now I feel disappointment when the Unreal logo comes up, oh another game with texture pop in, screen tearing and similar looking lighting.

Cryengine 3
https://www.youtube.com/watch?v=K7JV-5a0Mdw
https://www.youtube.com/watch?v=JWvgETOo5ek

Unigine
https://www.youtube.com/watch?v=D8weFu2f6QU

https://www.youtube.com/watch?v=HO8MRT_Ymhk

So far, demo that impressed me the most is Deep Down - so my vote goes to Panta Rhei.

Bitsquid
http://www.youtube.com/watch?feature=player_detailpage&v=yU6lkhjcOp4

hard to say since the frostbite 3 stuff is real gameplay and the rest just tech demos where we have no clue how they games will look like. i'm sure a frostbite 3 engine demo would also look better as the battlefield gameplay. same with the engine used in killzone.

Didn't even know about the other two engines beside cry, alright adding now.

I hope CDProjekt show off RED Engine 3 proper soon, apparently they plan on licensing it and everything. And I am very interested to see their new rendering engine.

Also on the open world front there is Avalanche Studios' Avalanche Engine 3. They did some amazing work on Just Cause 2 in terms of optimisation. 

Ya, I beleive the witcher 3 will be running on that engine. I especially can't wait to see some Cyberpunk 2077 gameplay.