why was the change allowed
it's not even an art style thing, the entire design was changed. the helmet is vaguely similar to the old one but the rest is completely different. it's absurd
It is an art style thing. Look at all of the environments, the other SPARTAN models and every other piece of art. The Halo 4 Master Chief's armour fits into that world, but his old armour-style wouldn't.
The change was made probably because:
A) 343 wanted to have their own distinct style so that people would associate the new Halo with them.
B) 343 wants to tell a new story, and they were taking influences from Ninjas, cyber-punk and other places. You can see this reflected in the SPARTAN's boots, as well as all the lighting and the music.
C) 343 wanted to push the graphics engine to see just how many polys they could throw at it.
D) Microsoft asked 343 to take Halo in a new direction, including the art and gameplay. Microsoft seems to be making a lot of changes recently, including stuff like Metro and Cortana.
I think 'B' is the main reason. I noticed a lot of new influences when I tried out Halo 4.