I think it would be cool if...
- it started off with MMO style character creation. I think the key to keeping people interested is lots of possibilitys for different characters. The problem is keeping it balanced.

-Then it would be like diablo 2 / first person shooter. You would enter dungeons or battlezones from a third person world, but if you used a gun, you would frag fps style, then if you were a matrix controller or archaic hand, you could use either third or first person. You'd go through dungeons fragging many units, and of course there'd be items and such. You could gain skills, and skills in weaponry would change the actual spray of your gun in fps mode.
-It could also have a great story line outside of the dungeons as well, where all sorts of other skills could be utilized, from espionage to ionization engineers.

-Different planets is almosta given. But they would probably have to be just the dungeons, unless you want to create many seamless worlds the size of WOW. That would be awesome, but probably expensive and not practical.