For the most part I think Weapon Master builds are worthless, so I set out to see if I could leverage a bit more from this feat-hogging class. This is the result:
The Swordsman | NWN2 Character Builder
Feats are by far the worst part of the Weapon Master class.. this build leverages at least a portion of those feats for the Shadow Dancer class. (..Dodge and Mobility.)
Another problem is the need for Intelligence of at least 13 (from Combat Expertise), so I figured why not ditch the more traditional Strength build in favor of an Intelligence build? The Swashbuckler gets you part of the way there via Insightful Strike for your damage modifier. At Epic level 23 it concludes with Combat Insight.. (..and because the Weapon Master required the feat Combat Expertise, I didn't have to spend a second additional feat to get it).
With both Insightful Strike and Combat Insight while wearing a +8 Intelligence modifier helm, you'll have +16 damage on non-critically immune opponents. Add to that as much as +8 from an enhancement bonus, +6 for Epic Specialization, and 6 from a rapier - and it all stacks pretty nicely for a critical at x3 damage multiple. (..36 * 3 = 108.) It should also happen very frequently due to the low threat range of a rapier/weapon master and the high attack numbers for this build.
Speaking of high attack numbers, not only is the BAB high, but the attack bonus is also very high because of the very High Dexterity with Weapon finesse (..and a rapier). Further, an attack from a hidden state (using HiPS), effectively strips away most armor class bonuses - making it *very* easy to hit any opponent from a hidden state (..and usually scoring a critical in the process).
Then you have a few other "extras":
Whirlwind - it's not as effective as with a two-handed weapon, but at least the Rapier is as long a weapon as you can get while still benefiting from Weapon Finesse. It gets more useful at Epic levels and with the very low critical threat range it *may* be as useful as an excellent "Cleave" type build.
Disarm - your attack bonus is very high, so your Disarms should work most of the time. Conceptually a really good swordsman *should* be able to disarm an opponent, no?
Expose Weakness - you are going to be enhancing Dexterity for the attack bonus AND for the AC bonus.. so why not get a fair chunk of damage reduction penetrating damage to "boot"? At a full 28 in Dexterity with a +8 Dexterity belt you'll have a net 36 in Dexterity. That provides not only +13 to your attacks and AC, but also an additional 13 damage per round for 5 rounds to your opponent with Expose Weakness. :mischief: