Thanks for all that research! I didn't know those websites.
In the meantime I've started digging through Wikipedia's article on
machinima, didn't know that Spielberg used "Unreal Tournament"
Quake movies are no news to me. My buddies used to make videoclips out of "IL-2 Sturmovik". I'm just surprised now it's called film making and art!
You mentioned other genres: I've started looking for platformers.
Duke Nukem (the first one!) has option "play user demo", but how can I record one?
Abuse seems to have demo recording feature, but only in level editor? Anyone more familiar with these two?
By the way, I've updated the group description (pending) with extra info & to make it more clear.