My first game on PC was Red Alert.. good times. I liked Red Alert 2 as well. Age of Empires series is also great and can't say i disliked StarCraft either.. Also played Warcraft II and it was okay as well. (Funny thing is that i own Warcraft III as well, but never played the actual game, only custom maps).
What i don't like about RTS games or pretty much any games with online multiplayers is the idea of playing against random people. I have no motivation to "improve" if i end up playing against another guy every time. I want to be able to tell if i have improved enough to beat the guy who i couldn't beat before.
So that said, if anyone feels like playing AoE 3, i wouldn't refuse the challenge even though i was never good at it and haven't touched it in years.