Avernum 2.
Avernum 1 is okay, but looking is a right pain in the, I use the mouse for everything :\
Avernum 3 was the first one I played andalso the first I won, but the first 2 main quests are way too easy, and all the quests aren't connected enough. I mean, you can win the game only completing 3 of the 5 main quests.:\
In Avernum 2 all the main quests blend together, and you have to play them all to win. Plus beast ceremony is dang useful, divine aid in A3 is so annoying only using it once a day