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.
Used to play these old real time strategy games based on The Lord of the Rings made by EA. Battle for Middle Earth 1 and 2. Played the shit out of those and their expansions and mods for years. Never as polished or advanced as the big RTS stuff like Starcraft but I loved and still love them. The graphics and enemy AI of course look their age almost 20 years post release. What I wouldn't give to have them remade or remastered or something. EA doesn't have the license anymore and its out of production so it's hard to get legitimately these days but you can pirate them all just fine which is nice because I think I lost a few of the installation CDs. I'd give any thing for a modern remake with a better engine and graphics. I feel like RTS games just don't get made that much anymore 😕