Have you all played Dune 2? In 1992 that masterpiece started this genre called RTS. The game gives player an outstanding feeling, combining the events on the battlefield with some nice music which is calm when there are no gunshots and which become very aggressive on a big fight, raising your adrenaline.
Then, Blizzard came with Warcraft I (Orcs&Humans) which was a good alternative for all those who finished Dune 2. Unlike Dune 2, Warcraft had multiplayer support giving new perspectives in the RTS world.
Warcraft II came 2 years later, introducing Battle.net, where you could find many players to fight with. It had better graphic and map editor and much more campaigns.
Other Game companies were making RTS games like: Dark Reign, Total Annihilation, Age Of Empires, etc. But most of them were bad clones of those existing, one of the only with new elements was Age Of Empires, which introduced something from Civilization giving the game an unique feeling.
Z was good, came in with a new idea of territory control instead of buildings construction for getting units, but without multiplayer, the game did not live long.
And then the revolutionary Starcraft came out, many believe that even nowadays it is still the best game ever. One of the best AI ever, everything you need for multiplayer, supporting up to 8 players in the same time. But above all, the game had 3 completely different races to choose from. For the first time, they were completely different in both looking and administration/strategy. So now it was like 3 in 1 game, after you play with Zerg, you get the Protoss and you feel like you are in a new game.
Rise of Nations, Age of Wonders, Empire Earth, Earth 2140, War of the Worlds, etc etc.. All these were a complete waste of time from the developers.
However I should not miss Dungeon Keeper which came with new elements and new feeling but the games lack in units' AI, specially on multiplayer when you meet the opponent and things get too chaotic.
Settlers series is good, but has too many bugs and some problems in battle where you cannot control your soldiers well, giving you the feeling that you are not really in control of your army. Kinda frustrating.
After Warcraft III - Reign of Chaos which brought in some RPG elements into RTS making the game attractive, no other strategy game had success. Why? Because the developers are working only on graphics and only on bringing new units, 100 new units, 1000 new units, addons with even more units, maps but nothing new in the game engine or in the strategy.
They all are obsessed in introducing 3D in Real Time Strategies and even Turn Based ones. Hellooo!!! People who play such games are not very interested in the 3D elements, they want something new in the game, to make it attractive!!! Waste your 3D on shooters and RPGs where people might appreciate it, but not on strategies.
Some of you probably wonder why I did not mention Command&Conquer series. It's because they are not good, they are Dune2 clones bringing only new units, nothing new in the feeling part of the game. A good strategy game is tasted in 2 phases: 1) You explore the game and it's features playing single player scenarios or campaigns, unfortunately after some time you get bored. 2) You start making strategies and play with other players always improving your style and never getting bored because the games turns out into a sport like ping-pong or chess or even soccer from the coach side of view. The games which are poor at 2nd phase, die fast. Therefore I would make a top 3 of best RTS ever:
2) Warcraft III
3) Dune 2
Yea, yea, no multiplayer(at least not in the original version) on Dune 2, but it deserves it's place since it was the first of his type.