Useful point: The lower the Dismember Threshold is, the easier it is to dismember Uke. If you want to do some damage, and are finding doing so difficult, lower it.
Also, read the manual the comes with the game. It can really help.
"Call yourself alive? I promise you you'll be deafened by dust falling on the furniture,
you'll feel your eyebrows turning to two gashes, and your shoulder blades will ache for want of wings."
If you're using instagib attacks like swords and he doesn't get dismembered, make sure that Dismemberment is set to 1. Keep in mind that the basic sword mod - the first on the list - isn't instagib.
"Call yourself alive? I promise you you'll be deafened by dust falling on the furniture,
you'll feel your eyebrows turning to two gashes, and your shoulder blades will ache for want of wings."