I totally agree about RA3; IMO I think it's a pretty good RTS. Though I've not tried SC2, I was kinda disappointed that it didn't have anything new in-terms of gameplay except for better graphics, new units, old units with better or upgraded utilities.

Warcraft 3 was something I would say that's revolutionary; the hero system brings RPG elements to the RTS genre which adds to the gameplay dynamic. Though I have to say that the hero system has it's draw backs too, keeping a hero alive(which is one of the most important thing in the game) was not newbie friendly and many casual RTS gamers where turn-off by how much the game demands on micro-managing your units. It was truly only for those dedicated enough to practice and hardcores.