Here's a thread to post your favourite character builds. I'll start with the build I'm currently using:
Mutated human
Arconaut
ST: 15
AG: 20 (18+2)
TO: 17
IN: 17
WI: 15
EG: 20
[ Mutations ]
Esper
Unstable Genome (4)
Force wall
Narcolepsy (D)
Fun with lots of unstable genomes! The build is quite weak initially, but scales nicely. As I level up, I put all or most of my stat increases on Ego, buying new mutations whenever I can whilst waiting for the unstable genome to tick in.
Stat- and skill-wise, the high Agility makes for a pretty good fighter with short blades and firearms. Get the Shank skill as early as possible, which would be level 6. You'll be able to get Tinkering at level 12 at the latest. (If Tinkering isn't so important, you can lower Intelligence and give some other stat a boost.)
Narcolepsy: If you want Esper in addition to 4 Unstable Genomes, and still have 3 points for a useful mutation, you have to take Narcolepsy as your defect. In my opinion, it's actually not so bad; it's only directly killed me once. Falling asleep during battle occurs rarely, and all it means is that your enemy gets one free hit, which usually isn't a big deal. Another caste that fits well with a narcoleptic esper, is Apostle, since your follower will at least partly offset the negative effects of Narcolepsy.
Force Wall: There are several feasible starting mutations. I choose Force Field because it's a great defense _and_ weapon from the very first fights and through the entire game. Even though you start out a little squishy at level 1, you can already take down baddies like salthoppers, using a force field and bow and arrows. Buy a firearm as soon as you can, though! Even a musket in Red Rock can be a life saver at times.
It's also feasible to forego of Esper, which leaves you with an extra mutation point and a wider range of defects/mutations to choose from. This particular build benefits from a focus on mental mutations, though. As you level up, you should avoid getting too many physical mutations that you must spend points to improve later on. Rely instead on a high Ego and as many mental mutations as possible.
I had a really formiddable run with Helping hands, multiwielding short blades. Things got weird when I found a carbide wristblade and some polymorphic gel. Suddenly I was septuple-wielding flaming carbide daggers, instakilling cragmensch and the like. It could happen to anyone, I guess.
As always,
Minotauros