CS:S isn't an RTS, but it's very fun. I've been a class-based CTF/DM'er since my birth and I totally didn't care for Counterstrike on Half Life 1, but something about CS:Source on the HL2 dealy is just extremely better, and extremely fun. Moreso than it just looking a billion times better.
I seriously suggest CS:S. Don't play on non-protected servers, tho, because hacks are abundant. Most servers (good ones anyways, hosted by major pplz) have the built in anti-hack turned on, and your set for a good game and a good time.
There is a new Star Wars RTS coming out next year in Spring that just looks totally badass. I'm not a SW freak, but WOW! Check it out.
I quit FFXI, WOW, Lineage2, etc, etc... MMORPGs ... you will reach a point, if you already havent, when you will realize the "fun per hour" ranking of MMOs is TERRIBLE compared to like CS:S. In 5 hours, you can have tons of CS:S fun, mIRC it up or teamspeak with some friends, and do hilarous stuff and feel rewarding. Or, spend 5 hours in WoW running around like a moron taking some elf his nuts and staff to earn half a level. :saywhat:
Eat me.