There is a kind of game people say no one will make, that they don't know how, but it has in fact already been done, and has been so popular that even to this day people still play and mod it.
This game is battle zone 2. It is safe to say its the only one of its kind that successfully blends the dynamic worlds of FPS and RTS effectively making a new hybrid genre known as an FPRTSS
Games like battle zone 2 are extremely rare and dying quickly, battle zone 2 is currently in good health but has lost many of its regulars over the years, atm there is less then 100 people a day.
BZ2 is a game where you drive hover tanks, construct bases, build more tanks (thugs), and attack the enemy base, I'm sure many people would enjoy the FPS and RTS qualities of the game, the storyline in campaign mode is solid, and the multiplayer is beautifully crafted.
The game itself is free (can be torrented from MANY sites) and the people in it are very friendly. The game has extremely light requirements, even IBM's can run it (win 32x can run it O.O)
It only requires 500mb of active space on your comp and the patch (public beta 5.1) only requires a little more, if you feel the need get RD's G66 variant as well, its very fun. (AND HARD!!!)
I forgot to mention that this games current home is BZuniverse. Go there to find out more information, how to get BZ2 how to mod it, and anything else you need.