ok, i've been thinking and: 
  
mongoose: no guy, AR guy, Rocket Guy 
warthog: front bumper (better ram), LAAG, gauss, rocket, rocket passenger 
falcon: front turret, side MGs, side grende launchers, transport less troops than pelican 
covenant leader powers are changed to be like UNSC powers: spirit transport, glassing airstrike etc. 
play as the neutrals 
new neutral: promethian - knights, crawlers, watchers 
change the UNSC anti infantry from flamers to snipers 
swap cyclops for mantis 
add in mammoth that does the same as the elephant but spawns warthogs/mantis' instead 
more of the single building pads 
add upgrade buildings: infantry- training centre, vehicles (air and land) -garage or repair shop 
  
whadaya think, eh?