Something Star Wars-like, with different spaceship classes, lots of weapon varieties, alien species with different attributes, etc. But the Jedi would be too overpowered, so you can leave them out, key as they are.
And, integrate more fundemental parts of RP's as well. For example, if the setting is a war, you may want to try your hand at and EXP and leveling system. I've attempted it, though, and it's a huge headache, so you can avoid that if you want. Also, I've been itching for an RP with a good class/subclass system.
