Took a look at what Pathfinder does to beef up some underpowered classes and adapted for NWN 2. I've given these classes capstone abilities at level 20 that would make it "worth it" to take these classes to 20 instead of just making them part of builds.
Fighter
3: Dodge
9: Defensive Arts
12: Elusive Target
19: Damage Resistance 5/-
20: Weapon of Choice, Increased Multiplier
Basically, the fighter gets AC feats for free instead of having to spend feats on them. This approximates the increased max dex bonus in armor Pathfinder fighters get. For going all the way to 19, fighters get DR 5/- because they're seasoned badasses, and going all the way to 20 nets the fighter one Weapon Master ability.
Paladin
5: Divine Bond (sword properties or Special Mount summon)
8: Immune to charm spells/effects
17: Damage Reduction 5/Evil, changes to...
20: Damage Reduction 10/Evil
Paladins are in a weird spot between damage dealer and tank. Most of their offense comes in a burst, and their durability is very reliant on short-lived buffs. The Divine Bond is a nod to PnP, recognizing that part of the class' balance comes from having that ability. The Immunity to Charm spells/effects is in Pathfinder, and I like it.
At levels 17 and 20, the Paladin receives abilities that recognize her commitment. She is such a pure being that only weapons wrought of evil can harm her. This improves the paladin's staying power, and it's certainly not over-powered, given the DR of a certain other class with much more power at its disposal.
Rogue
2: Weapon Focus
4: Stealthy Feat
8: Dodge Feat
12: Mobility Feat
15: Skill Focus: Search
17: Skill Focus: Disable Device
20: Death Attack
Pathfinder rogues get lesser rogue talents before level 10, so I added in these extras to allow the rogue some better combat and stealth efficiency and to give them more freedom to explore various builds. The point of the level 15 and 17 feats is to make rogues the best trap spotters/disablers. The level 20 death attack is a reward for taking the class all the way to 20 and forsaking the HiPS offered by Shadow Dancers and Assassins.
Barbarian
4: Rage heals 1d8 + CON Mod.
6: +1 dodge AC while raging
8: Rage heals 2d8 + CON
10: Second Wind Feat
12: Power Critical, +1 (+2) dodge AC while raging, Rage heals 3d8 + CON
15: Freedom of Movement while raging
16: Rage heals 4d8 + CON
18: +1 (+3) dodge AC while raging
20: Rage heals 5d8 + CON, Haste while raging
Barbarians suck. They get HP but no AC to protect that HP, and they don't have the utility that fighters do or the damage that Weapon Masters do. The Rage has had some things added to make the Barbarian more durable while raging, and at level 20, he gets Haste, which is tremendous. Second Wind at level 10 allows the Barbarian to build without wasting a precious feat on that requirement and then transition to Frenzied Berserker for the full 10 levels, if he so chooses.
Fighter
3: Dodge
9: Defensive Arts
12: Elusive Target
19: Damage Resistance 5/-
20: Weapon of Choice, Increased Multiplier
Basically, the fighter gets AC feats for free instead of having to spend feats on them. This approximates the increased max dex bonus in armor Pathfinder fighters get. For going all the way to 19, fighters get DR 5/- because they're seasoned badasses, and going all the way to 20 nets the fighter one Weapon Master ability.
Paladin
5: Divine Bond (sword properties or Special Mount summon)
8: Immune to charm spells/effects
17: Damage Reduction 5/Evil, changes to...
20: Damage Reduction 10/Evil
Paladins are in a weird spot between damage dealer and tank. Most of their offense comes in a burst, and their durability is very reliant on short-lived buffs. The Divine Bond is a nod to PnP, recognizing that part of the class' balance comes from having that ability. The Immunity to Charm spells/effects is in Pathfinder, and I like it.

At levels 17 and 20, the Paladin receives abilities that recognize her commitment. She is such a pure being that only weapons wrought of evil can harm her. This improves the paladin's staying power, and it's certainly not over-powered, given the DR of a certain other class with much more power at its disposal.
Rogue
2: Weapon Focus
4: Stealthy Feat
8: Dodge Feat
12: Mobility Feat
15: Skill Focus: Search
17: Skill Focus: Disable Device
20: Death Attack
Pathfinder rogues get lesser rogue talents before level 10, so I added in these extras to allow the rogue some better combat and stealth efficiency and to give them more freedom to explore various builds. The point of the level 15 and 17 feats is to make rogues the best trap spotters/disablers. The level 20 death attack is a reward for taking the class all the way to 20 and forsaking the HiPS offered by Shadow Dancers and Assassins.
Barbarian
4: Rage heals 1d8 + CON Mod.
6: +1 dodge AC while raging
8: Rage heals 2d8 + CON
10: Second Wind Feat
12: Power Critical, +1 (+2) dodge AC while raging, Rage heals 3d8 + CON
15: Freedom of Movement while raging
16: Rage heals 4d8 + CON
18: +1 (+3) dodge AC while raging
20: Rage heals 5d8 + CON, Haste while raging
Barbarians suck. They get HP but no AC to protect that HP, and they don't have the utility that fighters do or the damage that Weapon Masters do. The Rage has had some things added to make the Barbarian more durable while raging, and at level 20, he gets Haste, which is tremendous. Second Wind at level 10 allows the Barbarian to build without wasting a precious feat on that requirement and then transition to Frenzied Berserker for the full 10 levels, if he so chooses.
Comment