The Unreal Engine 5 Feature Highlights is up there for me, the music makes it so incredibly epic, gives me goosebumps:
And yeah, the 2011 Wii U Zelda demo was gorgeous, I truly hope we see a Zelda game that looks like that but better in my lifetime.
The Unreal Engine 3 Samaritan demo also makes my shortlist; it still looks impressive today a decade later, which can't be said of many things in the fast-moving world of gaming graphics tech.
Another favourite of mine that I haven't seen posted yet:








