I can see why you want a HALO rpg, it has the coolest storyline I have ever seen-out of all genres. The Final Fantasy games have very deep and evocative stories, but the one in HALO is just plain cool. It would also neat to see what it is like being a marine and advancing through ranks, and commanding your own ships, or being abducted at age 7 and having to go through intensive boot camp type things to become a spartan (...yeah.. I read the books too
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But the thing that really made HALO was its gameplay. Way more open-ended than most first person shooters. I noticed in the newer 007 games the paths you can take are very small and limited. HALO allows you to experiment. Instead of having tons of scripted AI guys, they just placed a bunch on a field, and let 'em kill each other. You could either watch and pick off the remnants, or save all your marine buddies and lead an assault against a group of bad dudes.
HALO definitely needs to be reserved for the action genre, but having an rpg set in a science fiction galaxy-spanning war is definitely a cool idea. Take an overused idea and make it original and interesting.
Crazy Donut Productions
Current Project: KillZone