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.
I'm the exact opposite. Shogun 2 feels like the series' peak to me, but everything newer just has too many things that feel gimmicky. I don't like all of my units having special abilities, or my general being this super special guy. I don't want skill trees for my stack, I just want to move units around the map and stack up as needed.
RTR 7 is the best Total War experience for my time. Zoomed in map focusing on the mediterranean, your generals are also politicians so there's a constant tension between campaigning and administrating, a deep and meaningful system for conquest beyond just winning the battles. My dream strategy game is basically that mod but bigger and with better sieges.