Well I can see how medusa heads might not work in some areas, but man it would have been awesome for some of the platforming areas where it kind of gives you a 2d/3d perspective with Gabriel hanging. Probably would be tough since you can't hang and attack, but here is hoping for the sequel or perhaps DLC which would add that feature?
As for series staple enemies, I know we have a skeleton of sorts here and some armored knights. Bone pillars work in 2d, but from LoI, they don't really translate well on the 3d realm and aren't that big a deal to fight anyway. Bats need to make a come back though. From playing GOW we know they translate rather well in 3d. What else? I don't know if mermen are in this one or not. I am guessing not since I don't remember seeing them in the guide.
Now if you mean enemies from SOTN and onwards, then that is a lot of enemies to choose from. Some would work and others would probably not work too well in 3d and if they were included may not be as cool or as big a deal.