>>4899there's a part upgrade system
basically the systme boils down to grind for the parts needed to upgrade the various pieces on your suit
personally I got through the first leg of the story just fine with a zaku II with the only changes being the legs and chest were from the Fz, the head from the FS, a GM shield in zaku green (like that one from 8th MS team had) and a heathawk and zaku rifle
I kept them upgraded and was able to put out decent damage
some parts ARE harder to upgrade than others I haven't beaten the game so I can't tell you much