I mentioned Doom before. probably Half-life,Quake...American McGee's Alice.

Aliens Versus Predator, the only one developed was for Console, i never played it, and it looks horrible.
Oddworld, was planned to launch as an RTS known as the Hand of Odd. before being canceled, althought more oddworld games might lead to fruition, depending on the movie's success.
Ecco, the Dolphin. and I found the storyline very intriguing and the plot unique, that it has been overlooked by time...
The backstory entails, our favorite legendary city of Altantis, as they are genocided by the impending invasion of the Vortex. of course, knowning this they leave behind clues, to which a Dolphin to save the ocean by going back through time....
Well it would be awesome to see that as an RTS translation.
Who wouldnt want to see hypertech Altantians versus the slimy Vortex aliens? Not only both sides are very different and would slug out exotic weaponary, but the locals themselves would be very visually stimulating and require different tactics, despite relying much more on Naval warfare...battles can take place either on vaugly prehistoric landscapes, dystopian beaches, or even submerged in the depths of the oceans...kinda gives a new meaning to trench warfare..