Let's think about the key RTS milestones in history...
I could start with the Peter Turcan games from the 1980's but I don't want to encourage masochism. Let's set year zero at:-
Dune 2 - I completed this 3 times once as each race. Great game and the progenator of everything that follows. Introduced: mini-maps, Different Factories for different unit types, Multiple same factories speeding up production, single resource gathering, expensive mega-weapons
Command & Conquer - Never really "got" this. Sure I own a copy but I've never taken the time out to finish it. Flawed multi-player but I won't get too cut-up about this as it was the first of it's kind. Introduced: Multi-player, One CD per side (so with one copy of the game you could play multi-player - probably sold more copies by word of mouth this way), Airstrikes, FMV.
Warcraft (II)- Been so long since I played this but it is important for a number of reasons. Not least of all proving that you didn't have to be Westwood... Introduced: The second resource, Humour, ships. Better balanced Multi-player, soon to become a Blizzard trademark...
Red Alert - By this time this came out I was rather bored with Westwood's glacial development. This was IMO more of a theme pack for C&C than a fully fledged new product so let's not mentionit or Dune 2000...
1997 was the golden age...
Starcraft - 3 completely different races with decent tech development. Still played competitively in Korea. Candidate for Greatest RTS ever. As is...
Total Annihilation - introduced proper height mapped terrain, sensible AI - (set your builders to patrol some time) Units that were not sprites and more emergent behaviour than it is fair to mention (e.g. commander kidnapping) Decent combined arms not just rock-paper-scissors and lots of units, yes, some of them were rubbish but enough weren't to make the game interesting. Lots of buildings including buildings to convert one resource into the other. Each factory could be queued up to produce different units. Builder units could be used to speed up production. Also introduced the concept of "The Commander" representing the player in the game and (usually) resulting in the loss of the game if destroyed (see also "Commander kidnapping" :). Also introduced the first great RTS add-on pack "The Core Contingency" which added a decent sized campaign, 100 IIRC new units and a map editor - now you're just showing off...
Dark Reign - overwhelmed by the competition but underrated Introduced rudimentary unit programming.
Age of Empires (II) - Introduced: Overkill numbers of races (9+), overkill number of resources (4) both of which enhance the user experience greatly and increase replayability. Multiple ways of getting the same resource - Hunting, Line Fishing, Berry gathering, Farming, Fishing boats. Solid candidate for the greatest RTS ever.
Cossacks - Introduced: Really big armies. Sensible unit formation. Regular 8 hour game times. Probably just a highly polished game and not innovative enough to be the greatest ever.
So before we go any further try to get a few hours under your belt in the following games:-
Starcraft, Total Annihilation, Dark Reign, Age of Empires, Cossacks. Then we'll have our frame of reference...