most rts's are creative in that way, if you look at certain rts's like starcraft, or even dawn of war you can see that there is some more creative mission ideas
Knowing how much the marines get shot up im sure there will be some good medi-vac missions :)
And the UNSC wasnt losing All the time before the spartans showed up, the marines may be cocky and sometimes annoying in the FPS's, but they can obviously get the job done :P
just my two cents :)