Old school RTS. Unit customization was incredible even by today's standards. Didn't come together well though, it sucked
Basically you run a mercenary company and accumulate money for completing missions. You use that money and other resource(s) during your missions to build units. Between missions you use your money for hiring scientists, researching and unlocking techs.
Here is where one of the best freaking RTS portions come into play. You use the tech you have researched to design your own units, or upgrade existing ones. You pick a base unit or chassy, like the "jeep." It will have a certain number of points that you can put weapons on. Then you add, engines, armor, weapons, computer chips (for sight), and other equipment. So say you slap the largest gun you can on the jeep (like a mini-gun) biggest engine you have, best computer chip, and very light armor and you have a reasonable land scout that pops like a balloon but can get the jump on some units and mow down infantry or be a problem for light aircraft.
I have yet to see any other RTS add this depth of unit creation. Frankly its the kind of feature that would set other RTS's apart from the rest of the pack. Lets face it. The market is saturated with RTSs these days. Some are good, some are bad, some are ugly. But, the only games you can find unit construction options in are strategy games. I would love to see this feature reawakened and in more games. Sure, not everyone is interested in it (like I am) but think of the possibilities and new dynamics in multiplayer games.
Ok, I am slightly stretching the truth. Cyberstorm, and Cyberstorm 2 you could customize your units somewhat. I admittedly have not played all the RTSs out there either, I'm just trying to let people know what I like.