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.
Oh I thought this meant politically. I quite enjoy GTA:SA and IV but fuck me all the political satire was piss poor from the start and it still somehow manages to have aged even worse