My favorite build right now is a roleplay heavy set of mutations and skills: I take the beak deformity, and with wings and heightened speed and nightvision. I play this "bird person" as an arconaut, and getting started can be surprisingly difficult! I mean flying is strong, but no face or back slots plus very little health requires some strategy for those early levels. Once you get enough arrows or a rifle, you can take most anything on the ground as long as it can't shoot you and you avoid pissing off the giant mosquito swarms. Falling down is still a death sentence, though, and your wings are useless underground. However, If you're smart about it the flying bonus to wayfinding lets you rush up to the stiltgrounds and pilfer / purchase lots of goodies.
I'm still pretty new to the game, but the unique setting is probably the biggest selling point for this game. Roleplaying is a much smoother experience due to the item design that encourages both flavor AND utility, while letting minmaxers do their thing if they so desire. I have fun visualizing this bird person flapping about, a rifle strapped to his back, two daggers and countless grenades strapped to his belt. It's pretty good when he talks to this one character who I've forgotten the name of, and she blames "the birds" for some massive catastrophe or something. *flaps angrily out the hut*
Other builds include a farmer cursed to mutate uncontrollably, a precog scholar who can experiment his way through the unknowns of Qud, and a dual-weild Syzyrgior (?) who acts insufferable around lowborns.