It's quite good.
The subquests are sometimes a little tired, but tend not actually to be that FedEx-like. Many of them are actually quite interesting.
The main plotline is quite complicated, but very interesting. It also allows two main paths from around the middle to the end (good or evil)
Character development is very good: the character generation system is extremely flexible, and there is a great deal of scope for non-combat characters: a Charisma-based diplomat could be very effective in Arcanum.
Graphics are a little old, sound is hauntingly good.
The NPCs are well-written (well, the voiced ones at least)
On the whole, I enjoyed it. I wouldn't jot it down as all-time favourite, or anywhere approaching that, but it seems ok.
Alternately, try Planescape: Torment. It's about two years old now, so a little weary, but you can get it really cheap and in terms of character development, plotline, immersion and character interaction it's still a classic.