@Franny
Call me anything you want, just don't cross over too many limits.
@Satis
Sorry omnipotent one.
*schemes on elaborate ways to take over the forum*

Maybe it's because of your party type? Whenever I fight the Shadow Dragon, I always go for mass offense and he goes down easy.
Your party is spell-oriented, but the defensive/summoning type (druid+cleric spell majority).
The Shadow Dragon also starts releasing his deadlier arsenal only when he's not in too much pressure (i,e. Shadow Dragon breath, rarely seen).

Btw,
The Blade Guide's
It's a long read, so you might wanna skip the basics and just head down to the great stuff.

actually we did that... summoning is a huge part of our attack (and how we whoop up on most people). Mainly fire elementals, but I also have the efreeti bottle and cerebus. And animal summoning II (the bears).

Minsc and I (2 rangers) would run in and whack on the dragon physically, while yoshimo uses arrows and everyone else just nailed him with spells and/or summoned stuff.

Except, he'd use his wing or breath attack and freak out either minsc or me every time. Half the party would be feared and I'd usually end up getting one guy's a$$ handed to him... then have that guy run around the screen like a pansy as I try to drink healing potions, with this huge freakin' dragon right behind him. Blah...anyway...we finally killed him. I'm thinking firkraag will wait until after the underdark.