How to vary gameplay
Imagine joining a game of NS, but at the start, there is a slight planning phase. Marines login, and are in a ship/transport/milky darkness, its time to choose commander. Commander takes control and decides how the game starts for marines.
-Rapid Deployment. first 5-10 minutes, marines spawn fast and often, death means nothing, upgrades are expensive, and marines move quicker, shoot faster. Their damage does little to structures, unless concentrated. The key word here is Mobility. Entrance spawn points across a map may be used to increase mobility, and may be changed FAIRLY often, but not TOO often.
-Fortified. First 5-10 minutes, marines are in Alamo mode, defending what little they have, they start out with 2x "res" feeding structures but what little they have is fruitful. Their "res" is collected faster, and equipment is cheaper(welders, grenades, mines) (upgraded LMGS, more ammo capacity than normal, inaccurate). Their new structures are easy to defeat at first, but as time goes on they enter a fortified mode and become stronger(not impossible to beat, cutting a link that fortifies breaks the fortification
I like the rule of 3's and I can't think of another one here. There is the aggressive, and defensive, and I think there should be another mode that is out-of-the-box, and then maybe a "normal" mode where little modifications are made.
Aliens would get a similar system, and that one is probably the most interesting to think about creating. It should focus on the strengths and weakness and the lore of the aliens.