I think they are a good thing, since in general you get better compatibility with more esotheric hardware, for example i’ve seen people run godot games on raspberry pi boards, which is pretty nice; also as you mentioned doom and 0 A.D., both of them have prolific modding communities because it’s easy to make mods when you have the source of the game, and in the case of doom in particular the fact that it’s open source allowed people to build lauchers to make it run on newer computers without needing dosbox and co. To even have a chance to play.