You need to first realize that there are many kinds of flavor’s of RTS games. Some types you may never master and others you might become the undisputed champion of.
Here are some properties you can use to categorize an RTS game:
Micro Management aka Heavy Micro or not:
Do you need to manage your troops heavily. Move this unit here and that one there? I do not mean groups of units, but individual ones.
Examples of Heavy Micro games:
Starcraft, Warcaft III
Examples of nearly Micro Free games:
RoN, AoE series.
My personal Preference: I can not micro units very well. My neural circuity simply is not up to the task. I was clearly shown this by watching Cecil (if you watch WCIII replays, you will know who he is) playing a few games at UCF LAN (in Orlando Florida). No amount practice could help. He would switch camera locations, issue orders, and move on before I could even comprehend what I was looking at. I do not play Micro heavy RTS games unless I am playing against equally micro gimped players.
This has two aspects is how difficult it is to manage an economy. The simplest is to simply have a single resource and just throw more peons at the resource to get more of the resource.
The second is how the cost of units and structures impact your economic choices, especially with the rush. If putting together a rush only has a minor economic impact, then I would rate this second aspect as ‘simple’ because there no hard economic choices to make.
Examples of Simple Economic games:
C&C Generals, RoL, Starcraft, BFME2, or pretty much any RTS to come out in the past few years.
WCIII is kind of in the middle between complex and simple, although it is much closer to the simple side. A lot of rush tactics and long-term tactics do impact your economic decisions.
Examples of Complex Economic Games:
There are only some old games I can think of: Warcraft II and Total Annihilation (expanding your economy was not trivial, and you had to allocate a significant part of your economy to expand it).
My Preference: A complex economy. I like to have the economic impact of tactical and strategic decisions weigh heavily on players.
Unit mix and complexity:
This aspect is on both the quantity and quality of units. Does an RTS have a few kinds of units or a lot? Do monolithic armies work well (mass hydras, nothing but medium tanks, etc…) or do mixed armies do much better (aka the whole is much greater then the sum of its parts).
Examples of ‘simple’ games (few unit types, unit mix does not matter much or at all):
Starcraft, RoL, Red Alert 2, Kohan series (Each squad is forced to be mixed, but if you just look at this as a super unit, then there is no big advantage to mixed unit types).
Examples of complex unit mix games:
Total Annihilation: Huge array of units, and yes, their subtle flavors really did matter. Mixed armies were vastly more effective then monolithic ones).
C&C Generals: For the most part, mixed armies were much better then monolithic ones, however, there were a few imbalances that broke this rule such as mass Quads (gla), mass listening posts (infantry generals only), and mass stealthed choppers (airforce general only).
This represents special powers you could use that gave you a very strong advantage or let you do something ‘special’. The most mundane and common is the super weapon concept as a nuke. Most RTS games have something like this, such as the nukes in Starcraft (terrans only), nukes in TA, etc…
Examples of weak strategic powers games:
Warcraft Series (none)
Rise of Legends (one very weak power per nation, with the exception of the giant gun the Vinci can make).
Kohan Series (none that I can recall)
Examples of strong strategic games:
C&C Generals: Super weapons, Pop up tunnels, a myriad of air strike options such as fuel-air bombs, leaflets, EMP bombs, toxin bombs, instant rebel troop insertion options, the ability to make any group of units PERMINITLY invisible, etc… No game has ever come close to all the ‘toys’ you get as a commander.
RA2: Each side has a super weapon and a secondary faction power like a chrono sphere (lets you teleport anything anywhere), mind control, iron curtain (makes a group of units invulnerable for a while), etc…
My Preferences: I definitely like lots of strategic options. I want complex gameplay where you have to be creative. This is one of my prime reasons I love C&C Generals.
Anyway… Enough work time wasted here. You should look at this list and see what your likes / dislikes are and find a game that matches what you want the most based on that.