Warcraft 2 was my favourite game when I was about 9 years old. My brother and I would repeatedly borrow it from my sister's friend's older brother who must have been a big PC game guy (parents would never buy us games, we just borrowed them and played shareware that would occasionally run on my Dad's PC). Never played it online, only ever campaign. The tone, music and voices and art were just so spot on.
The warcraft games since then just don't appeal to me in the same way. I'm really indifferent to the 3D WC3/WoW graphics that most people seem to love and the atmosphere just doesn't seem to be there. I played a fair bit of WC3 tower defence with a friend but couldn't get on with the rest of it.
Adventures doesn't really fill me with nostalgia either, which is odd. I suppose what I like so much about WC2 is extremely specific even though I can't quite nail it down.
The only game that came close to WC2 for me was Warwind, another RTS from the same era the apparently only I played. There were loads of really cool little things that made it different from WC2, like how units could go inside buildings, and you could build roads and bridges. I found it incredibly spooky and dark at the time, even though there were loads of wacky touches. One of the races had 3 legs and 3 boobs, their workers would build stuff by punching their suddenly pneumatic fists against the walls, and they had units that rode motor tricycles in an otherwise ethereal fantasy setting.