Skill improving feats generally aren't very useful. In fact, there's hardly any need to increase Open Lock past a dozen or so ranks, since you can easily buy powerful Thieves Tools at higher levels, and/or get equipment that boosts the skill. And at high levels you'll never fail a persuade or bluff check if you just invest normal skillpoints into them, so epic reputation is pretty much a waste.

There are exceptions: bards can benefit from Epic Skill Focus Perform at epic levels, for example, and in online play taking (epic) skill focus on stealth or spot based skills can be vital if you want to use them. Not relevant for single player, though. Epic Skill Focus: Concentration can also be nice for wizards/clerics and the like.

Good combat feats include:
* Luck of Heroes: good save boosts
* Knockdown: the best active combat feat. Makes many fights MUCH easier. And knocked down foes can be sneak-attacked. Take this one.
* Improved Knockdown. Not as important, but it will let you knockdown big foes like dragons and giants. Recommended if you have sneak attacks.
* Blind Fight. As discussed earlier.
* Toughness. More hitpoints = good.
* Dodge: More armour class. Only works against one foe at the time, though.
* Power Attack/Cleave/Great Cleave: Helpful, though not THAT helpful. It's very good at low levels, and the improved version is pretty good at high levels, especially if you have few attacks per round. (i.e. you use a two hander or shield instead of dual-wielding) Power Attack isn't very good on its own, though.
* Expertise: Situational, but very good in some settings since it can make your character a great tank. Not really necessary in most single player modules, though.
* Weapon Focus/Improved Crit/Weapon Specialisation: As discussed, they're all helpful. But if you want to use multiple weapons you may not be able to afford them.

Not so good:
* Disarm/Improved Disarm: Not actually all that good, since for some reason many foes are immune even when they shouldn't be. (You can't disarm stock orcs, for example.) Which is a shame because it's a lot of fun to use.
* Other save-boosting feats: You can get much bigger bonuses from items, generally.
* Anything to do with parry. It's bugged.

If you're an archer:
* Called Shot: Not as powerful as Knockdown, but it works with ranged attacks, making it great for archers.
* Point Blank Shot/Rapid Shot: If you're an archer.

At epic levels:
* Epic Weapon Focus: if +1 attack bonus is good, +2 is great.
* Epic Weapon Specialisation
* Epic Prowess: for the same reason weapon focus is good
* Armour Skin: Armour class is just as important if not moreso than attack bonus.
* Great Strength (or DEX if you're Dex based): More hit chance, more damage
* Improved Sneak Attack: Only available if you're a high level rogue, but it can add up.

It's somewhat bugged when you have 4 or more attacks. (Which happens earlier when you dual-wield.)

You can never attack more than 3 times in a round, (except when you have Cleave or are making attacks of opportunity) so when you have 4+ attacks, your attacks start occurring in so-called "flurries" where multiple attacks happen at once. So a character with 4 attacks will get one "double" attack and then 2 normal attacks. 6 attacks will get you three "double" attacks, 7 will get you 1 triple and 2 double.

The problem is that if the first attack on a "double" flurry kills the target, the cleave attack gets aimed at the already-dead guy. Which is kind of useless.

If you have Great Cleave, this problem disappears: you simply get a second cleave attack on the next enemy after the useless cleave against the already-dead guy.

So: either take both Cleave and Great Cleave when you hit higher levels, or take neither.

A few notes:

* The expansion sare NOT meant to be played with the same character you play the original NWN campaign with.
* The original NWN campaign gets your character from level 1 to 16-18. It's also not very good.
* The first expansion (Shadows of Udrentide) is meant for a new character and takes you from level 1 to 12-14. It's fun enough and has some clever dungeon design.
* The second expansion (Hordes of the Underdark) is meant to be played with the character from Shadows of Udrentide and takes you up to level 25-27. It's pretty good: most people consider it by far the best of the lot.
* You can take Devastating Critical as early as level 21, if you're a Half Orc fighter/something who starts with 20 STR or a fighter/bard/RDD who gets strength boosts. Or both: a half-orc Red Dragon Disciple with fighter or (preferably) Champion of Torm levels. You then have to take an even fighter level as your first Epic pick. (Thereby getting 2 feats, letting you pick both Overwhelming and Devastating Critical.)
* So yes, you could get it in the Hordes of the Underdark campaign if you plan ahead for super-high STR.
* But honestly, Devastating Critical isn't much fun. Either it works and you kill everything you touch, or you're facing crit-immune stuff and it does nothing.