Warcraft 2 was fun at its time. Lots of funny things in the game, made it worth playing over its competitors in many ways (it still has a small competitive scene).
Warcraft 3 is probably the game with the most varied and fun user made maps of any game. There is some competition for the title but I think warcraft 3 takes it. (The game itself isn't good compared to its competition.) The only real competition in success of map making is probably Valves various games due to the success of CS.
D2 was good when it came out, there have been better dungeon crawlers before and after. D2 just did something right in its addition formula.
SC BW is a great, great PvP game, still worth watching today. SC2 is a meh generic RTS game after the first ~250 or so games. Then they made it hard to play custom maps that aren't the most popular, ruining their entire map making system (which showed the most promise of any recent game, still had some fun custom maps).