For me, I'd have to say Old School X-COM (UFO Defense, TFTD, X-COM Apocalypse to an extent). I love them in a way that I just do not enjoy NewCOM, but the interface was quite possibly based on the recovered works of a 13th century scribe, and is very difficult to get used to for an unfamiliar player.
Instant text speed, run button, and you knowing the game already to some extent.
Also the speedrunners can do the full 8-sanc run in under 2 hours.
fucking how