Here's my take:

Berserk attack
Probably one of the most powerful skills, though it's quite bad early on

Stamina Regeneration
Tough to judge, since all those regeneration skills don't do much in combat; probably really good though

May KO opponents
Does anybody know what KO% this adds? Anyway, on the fighter it's a bit wasted, since he is more of a killing machine

HP Regeneration
This CAN be good, since it compensates ANY -HP item you equip, but it's also somewhat wasted on the Lord, since he doesn't have a lot -HP items to equip

Cheat death
Okay, but somewhat overrated. At some point you get resurrection powders in abundance, so this is not really that useful. Quite good early on though.

Scouting
Useful I guess, but not really crucial (you can always search)

Ranged Criticals
Great stuff; this one makes "Ranged Combat" the ultimate skill for the Ranger combining the actual Ranged Combat and Ranged Critical Strike

Lightning Strike
Hard to judge, but I guess it's pretty mediocre, given how luck depended (and rare) it is.

Fearless
Fear is one of the less dangerous conditions, but immunities are always great.

Thrown Criticals
This is probably the only thing that makes Throwing weapons worth it for the Ninja, considering how little damage they inflict

Thronw Auto-Penetrate
Supports Thrown Criticals, probably really good

Effective while blind
Blindness is annoying, so this can be great especially against those Caustic Vines; I don't know HOW effective you are though... Does it mean you get some of the penalties (double damage when hit), but not all of them (like To Hit)?

Natural damage resistance
Very good, though maybe somewhat wasted on a class with Stealth.

Backstabbing
Killer! Maybe overpowered, especially with good swords.

Gadget making
Great of course, though to me this doesn't feel like a "Special Ability" (more like a basic ability for this very class)

Increased recovery while camping
It's twice as fast I think, which is quite useful, especially for magic users in your party

Pray for Miracle
It can be very useful, but its randomness makes it quite underwhelming. It's interesting, but often it's a round wasted on something that may not even work at all.

Potion making while camping
Mostly those potions are quite mundane, so I feel this is quite useless.

Remove Curse
Almost useless, since he can get the spell quite easily, and the ability is not really needed often

Dispel undead
Okay, but rather underwhelming compared to stuff like Banish... and even without Banish you're mostly better off using some other more effective spell

Mental condition immunity
For some strong fighting class this would be amazing; on the Psionic it's mainly useful to keep him sane in order to heal others... so yeah, probably not bad

5% bonus to all resistances
It sounds great, but at some point the Magic users will be quite resistant anyway due to their realm skills, so it's not that much of a deal I think