Well, I spent late last night finishing off the twins. (..hmm, that sounds a little filthy.)
I did manage to get enough experience from the various quests to get to level 17 as a Wizard, and one 9th level spell as a result. Didn't do me any good though.
Ex. Mass Dominate Person didn't work on a single opponent for the fight on top of the War tower, and this is despite having a decent Intelligence modifier of +6 AND both Enchantment focuses. Honestly, what's the point?
The ending battle sequence was about as absurd as it could possibly get.
EDIT: (I'm wrong here, wasn't paying enough attention to the story.) As a "starter" - Cambions (which the twins are), are supposed to be either Lawful Evil, or Neutral Evil - but they are supposedly serving a God that is predominately *Chaotic* Evil. Moreover their actions throughout are overall very chaotic (..virtual destruction of the Ten Towns, despite their claims, and use of the highly unstable Mythal).
The real "kicker" is that Madae is a NOT a cleric of Xvim, but rather of Cleric of Bane.

I don't know about you, but personally I find that appalling (even if Xvim is the son of Bane).
Then there is the "small" fact that you manage to kill their God before them.

(..or at least his temporary manifestation.) Sadly that fight with Xvim was more interesting than the twins. The one thing I didn't like however was the limited floor-space (..vs. the fight with the Twin's that had plenty of floor space with obstructions). In fact that limited floor space for the battle was a reoccurring problem throughout the game.
The final battle itself starts off pretty good, again - good floor space with obstructions, interesting help on both sides, etc..
HOWEVER, once you get rid of the help the game becomes impossibly stupid.
It's primarily all about defenses of your opponents (..those of the twins).
Madae has on Protection from Arrows. Umm, she is a 20th level Cleric of Bane (..again, moronic), and a 10th level Fighter. She does NOT have the spell Protection from Arrows - that's only from the Wizard/Sorcerer spell grouping. Ok, *perhaps* Issair cast it on her, but it seems a little hinky.
Madea's Protection from Arrows is a little hinky, but Issair puts on Anti-magic Field after a bit (..he tends to start with Globe of Invulnerability, Blue Fire Shield, and Seven Eyes). ..you know, Anti-magic Field because he is this powerhouse of a killing machine in melee with the structure of his classes: Sorcerer 20, Rogue 10, with an 18 in Strength and dual-wielding.

Why in the hell would a 20th level Sorcerer use Anti-magic Field? It's not like he pre-buffs with Haste and Tensers and THEN puts on Anti-magic Field. Further, BOTH seem to have VERY high Spell Resistance AND Saves, PLUS Issair has EVASION. Honestly, the last thing he needs is Anti-magic field. It's just beyond MORONIC. (..Issair picks up the gun, aims the but of it at me, and pulls the trigger.)
Next - both of the twins have an AC of 30 WITHOUT BUFF's or even Dexterity modifiers. Just how in the Hell do they manage that? It's not outrageous (or it wouldn't be but for the small fact that it isn't derived from equipment but is rather "Natural Armor" instead), but it's more than a little "ripe" IMO (.."ripe" as in: smelling bad, real bad). Without buffs there is one suit of Armor (in-game) that provides +10 AC with a max Dexterity of +2. Along with a max +3 in Deflection bonus. That's 25 AC. Something like the Golden Girdle would also add +3 to slashing weapons for a total of 28 AC against slashing weapons (only). That's still not 30 AC. Their AC is actually 35 (Madae) and 36 (Issair) due to their Dexterity modifiers.
The worst part however are the immunities.
Issair seems to be immune to everything but Piercing damage and Electricity (and secondary from Acid and Cold). He either resists or Evades most damage though.
Madae seems to be immune to everything but Blunt damage and Cold damage.
Maybe this is a Mythal thing? (..it's certainly not God granted - I put the hurt on him and cut-off his healing grant). It's definitely NOT a "buff" thing, and I don't see how it could be an item effect (their equipment was surprisingly weak after I looted their bodies). Moreover Cambions only have some *resistance* to fire damage, but the twins are completely immune to fire damage.
Worse - that Piercing and Blunt damage requires +4 or higher weapons, and if it's ranged weapons it seems to require +5 ammunition. (..you have to wait until Madae's Protection from Arrows wears-out to attack her with a sling - again a +4 sling or better. As far as I know there are no +4 or +5 throwing hammers.)
Even Worse - assuming you can meet those conditions, they still have 15 in damage reduction to each type that they are NOT immune to (..and this includes that elemental damage as well). Though after certain protections are "off" Madae takes 5 bonus in Cold damage.
Then there is actually being able to hit them.. At one point I tried out some melee on them - buffed with Haste, Tenser's, and Black Blade of Disaster (and several other buff's). Attack numbers were 40/35/30 - AND COULD NOT HIT EITHER TWIN.

WTF? Never mind not being able to *damage* them. In fact only with the Brillant Short Sword could I hit Issair in battle, and even then it was about one in 30 attacks, and more like one in 60 that did any damage at all (probably because it required a critical to get damage up high enough to over-come the 15 damage resistance). The "Brillant" portion of the Brillant Short Sword seemed to be not so brilliant after all.

(..probably because their armor isn't really "armor" - something more like Natural Armor of *20*

.)
..continued to next post.