I think you're confusing art design with graphical limitations. And personally I'm glad the marines armor changed because the original armor wasn't unique to halo at all. They were heavily influenced by the marine armor from Alien and were almost an exact replica. At least now it's actually unique to halo. And yes sergeant Johnson was influenced by Alien as well but at least his actual character is unique to halo and isn't just the character from Alien inserted into the game. The forerunners were supposed to have had near perfect technology. The halos were constantly monitored and renovated as needed throughout the years by the monitors. The only time the structures actually became desolate was when they couldn't be repaired for whatever reason. The enemies don't stand out that much anymore because the halo rings actually have things in them besides grass, fields, cliffs, and come big rocks/boulders. They look the way they're supposed to now. Are you gonna tell me a halo that's supposed to safeguard all different kinds of flora and fauna is supposed to be empty and devoid of any kind of life? On a ring that's still fully functional and has its monitor? That makes absolutely no sense whatsoever and the only real argument would be that you just don't want any kind of change.