I'd say this quest is a tough one, but fairly scaled, and pretty rewarding in both xp and loot. I only mind the length and the distance.
The main entrance is the real challenge, just like Gob. fort or Orog Fort, and it should be as in any defensive place. But once you're in, you're good to go.
As someone pointed out, it is a fort, caved in for protection, held by a warrior race. Taking this quest means you should be prepared to lose some of your teammates. You are told straight of that the duergar wiped out a whole dwarf clan...
It takes real preparation, not just buffs. It's not meta as you more or less know what you're getting into. Just like the other forts, it's a quest where pure strength probably doesn't work best: the enemy side is made of warriors defending a stronghold.
Just like in any stronghold attack, you need a plan: sneak tells you what to expect, if there are other ways, etc, then you plan ahead: who will do what, where, what spells are needed, etc. If the opposition is a barrier of 50 archers, charging in is not the best plan, period.
Thus the need for casters. It's one of the quests where they can make a real difference: mass damage spells, clouds, etc, can be really usefull by gaining you a few rounds, or summons immune to arrows, make everyone invisible so that everyone reachs the right spot before launching the assault, etc. IN ADDITION to the usual buffs, which never last long enough because the quest is long.
The folks who were wiped out by the quest were vets, with high lvl pcs, but i'd be tempted to say high lvl spawns do not require the same tactics as medium lvl ones. I've yet to see invisible/ sneaky people going all the way in, killing the boss and back out when it applies. There was a thread about flying chosen and ogres going the same way. High lvl means deadly spawns, which you are not required to slay.
I do know that dying in high lvl means losings months of play in terms of xp, and i know how that feels.
What i'm trying to say is that we are way too used to "buffs+charge= victory", especially vets. It's the same issue when a dm chimes in.
My two cents.