[kupoartist]

hmm...
UT2003 (the perspective, graphics and close range gunfights)
+ UT (the sniping)
+ Metal Gear Solid (the espionage and stealth)
+ System Shock 2 (the RPG like stats and the weapon adjustments)
+ a decent combat flight sim (i know of none, but what the hey...)
+ C&C Red Alert (strategy section)
+ earth and beyond (space combat sections)
+ homeworld (space strategy)

= one big development time, and an online game in which you would assume any or multiple roles in a galactic war, with your missions being assigned by real life commanders who assess your skill from an online database of your previous missions. You could play as many sides of the war - A soldier specialising in any section of weapons that you choose, a spy working alone to bring down the enemy within, a pilot (planet based, or space based) bombing and dog-fighting with the enemy or even the commander who orders the troops to the next objective... hell you could put in a load more things (naval combat) but it might get a bit silly if too crammed (outbreaks of zombies on your homeplanet which you must kill with a rusty crowbar!)