The original Warcraft remains my favourite in the franchise. I thought each subsequent version lost some of the character that defined the original game. Part of that was due to ever lower unit caps.
Nothing beat using peasants / peons to cut paths through the trees, as it allowed for resources to be used as tactics. Same with summoning elementals, which were immensely powerful but had to be used carefully due to their limited summon time.
However, I can't imagine wanting to go back to it without a significant update of the graphics and UI.