With the Unreal Engine, and many games (AoC, CoX, to name a few) that have good player customisation, it could be very well done.
Main things;
Height (long legs, short body, short arms, huge head, a different slider for each limb/part of the body please?)
Muscles
Body fat
Eye shape
Eye colour
Facial hair
Hair colour
Hair length (facial, arms, legs, head)
Skin tone
That's all I can think of. Add to the list by quoting it.
