I quite liked the Planar Sphere.
Those Halfling groups were pretty nasty and hard to deal with, especially the last group, and then the Demons! Crikey, that was interesting.
I ran into the strongest demon first, and used up all my remaining summon spells - fire elemental, some bears, and two nymphs. Then, I had Jan cast as many spells as he could get off, starting with Haste & Greater Malison. Most of my characters only seemed to be able to hit with critical hits. The best attack was Anomen's Bolt of Glory, for 40 damage in one go.
By the end of that demon, most of my characters had heavy damage and I had a single nymph left.
The funny thing was, I then found the second demon, started to run away, using the nymph as decoy, when the nymph successfully cast Hold on the Demon. I rushed back and clobbered him in about 20 seconds without taking any additional damage. Awesome!
On the third demon, the one with heaps of Imps and Mephits with him, I had to do a lot of running away, taking out his underlings with missiles as I ran. I had a couple of spells left including invisibility, but I had to reload a couple of times to get through it.