Ok, a little late with this post, but here is my opinion on the issue of the Grunt redesign-
Pros
-Lack of fully covered face is OK, they clearly are still receiving methane.
-Overall, the new art is fantastic and I love the new face
-likely looks amazing in motion
-did I mention the art over all is fantastic?
Cons
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Grunts are Arthropods, it is stated in the Halo Encyclopedia and Halo the essential visual guide.
As such, the fleshy hands and feet really do not make sense.
-Hands and feet now look more generic
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Feet now have a drastically different structure that ignore every previous Halo game. (Past games have had three front facing ‘digits/stumps’ with one on the back. halo 4 now has four forward facing toes)
-Overall profile/silhouette of the arms and legs are much more simple and uninspired
While overall I enjoy the new art direction, I do not like the huge changes to the grunt anatomy, namely the feet changing from stumpy appendages to a very recognizable fleshy foot with toes. (Interestingly enough, they seem to be influenced strongly by the Halo Wars grunt which you can see in the picture below) Grunts are established as arthropods, so not only does this change ignore what the past games established via art, it also ignore the physiology of a Grunt should be.
On top of the reason why the changes to the hands/feet don’t make sense canonically, they also happen to make the grunt look more like a generic monster rather than a unique alien species. Once again, the face and body are fine, as they stay close enough to what is established by previous games while making it their own, and in a fantastic way IMO.
Pictures to emphasize points above:
(at the very least the Halo Wars grunt tried to stay true to the digits on the feet despite turning them to toes)
and