There is a quest to be done but you won't be finishing it by just traveling in a single line.

Your character doesn't level up in the normal sence but can become more powerful by unloking the features of the other races.

Unlocked body parts are transformed automatically but you can change back in the "resting" options.  (or at least I hope to get that feature working somehow)

Aside from the forms of the other races you can also get DNA from a certain someones secret stash if you show him the right combinations of body parts and/or finish his special requests.  (this one will be hard work to implement but not the nightmarish kind of hard)

Not sure how I'll implement the balance system but as far as corruption vs. "true hero" I was thinking of each side earning means to get larger sums of form points per encounter like VORE (corruption side) and UNBIRTH (by which I mean the citizen or other becomes your temporary mother.)