you want action, you got action, massive number of troops and graphics like c&c, UBER fast action thall keep you on the edge of your seat. check out some of the recorded matches if you want.
http://www.hiverise.com/this one is sorta like a mmorts+rpg
http://www.boundlessplanet.com/build your empire and take on others with the added benefit of having alliances etc, get your own planet and mine resources and have that as your base of operations, this is probably one of the best MMORTS's out there.
don't want a huge dload and awesome gfx and shit? would rather have an in depth game bout space strategy? then play galaxy online from igg, dload is absolutely tiny and plays out sorta like a turn based strategy but empire building and all is like a cross between browser based games and good online games, difficult to explain, you should check out the gameplay videos and screenshots
http://go.igg.com/another classic, shattered galaxy, go here to get details and click on "tour"
http://www.sgalaxy.com/wanna try something from a major developer? try
http://endwargame.us.ubi.com/ tom clancy's endwar, only known MMORTS release from a major developer i think...
its a WW3 based games with 3 factions and a pretty damn good story to boot, gameplay looks good (haven't played it) but obviously it'l cost you some cash to buy (none if you're into piracy ofcourse)
one thing about this game though, the graphics are absolutely FANTASTIC! its recieved good reviews from most prominent reviewers like gamespot and ign at around 7.5-8.5
if youre serious about RTS gaming then DEFINITELY TRY THIS!
Another really good space based MMORTS is MANKIND,
http://www.mankind.net/this one has been there for like FOREVER
EPIC space and ground battles alike and an ever growing and improving community will keep you glued to this game for HOURS!
http://www.beyondprotocol.com/beyond protocol
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MMORTS is still a young genre hence there are just a handful of really good ones and most of those are space based (which isn't a bad thing)