Just finished and I have to say I was impressed. I played Crystal Souls years ago but completely forgot about Spiderweb software. A recent return visit sucked me into Avernum 5 for which I am grateful.
I liked:
Story - engaging with plenty of opportunity to divert into side quests
Use of humor - I still chortle about the 'dangerous alchemy shop located with usual consideration for civic safety in the middle of town' (or something along those lines).
Characters - many quite memorable, from the drunk Sergeant and the bored demon suffering from a surfeit of tedium to the dragon irritated with his nagging mother
Interesting fights - slitheraki horror, black horror, moref the shade, the pitmaster etc etc
Got one question that someone may answer. When you do in the despicable Gladwell there is a crystal to smash that releases a woman's spirit, apparently she looks 'familiar' to you. Who is that meant to be?
Anyway time to give Geneforge 4 a go.