Possibly have an alium-esque evolution tree for the human players? Nothing that actually makes them that much powerful, but the ability to have something with range in exchange for health, something tankier but slower, or something fast that can vent-crawl but is virtually useless at attacking?
Or, instead of stat changes, you have ones that can spawn the tiny versions, ones that ventcrawl or something, and ones that are just slightly beefier?
Just a suggestion, as I think that even only "everyone is a standard 'morph" would be crazy fun. If possible, you could have it to where necromorphs recover when next to the original node, and take brute damage when outside of their zone of influence (nondamaging area for the crew.)
I could likely throw in some help, but the last project I undertook died because I ran out of time/I lost half of the data, so... not sure. I can definitely do some random flavor items though.
Another idea is to build the necromorphs to be the exact same, but have three or four copies each pointing to different sprites and possibly flavor text, so that necromorphs are actually identical but look less bland. Can't say I've played Dead Space, or any other space horror/space zombie game, but I think the necromorphs did look different from one another.