Another organ that strengthens the immune system, and the organ produces a new hormone that kills cells that are mutated/cancerous on first site (the nervous system should send signals once messenger cells find it out).
Possibly the same sized brain, but a more efficient and compact one that is more effective and can calculate more than a supercomputer can.
Skin cells that are more resistant against the sun and it's harmful UV rays (assuming to ozone layers go poof).
New, more effective gastrointestinal track that allows vegetarians to exist without them killing their selves. Also allows a total-meat diet c:.
More effective buttocks that are only cuter on men.
