Maybe the best all around Avernum on steam (or at least until Avernum 2 and 3 show up in some form). If you've never played an Avernum it might be best to start with "Escape From the Pit," but Avernum 6 is probably a stronger game overall. Like EFTP it's very open world (although a few areas are closed off at the start), but it's biggest advantage is in its stat system, which uses the older skill based system that EFTP abandons in favor of a more simplistic skill tree model. Plus, unlike Avernums 4 and 5 (which had trouble justifying their existences plot wise), the writing is great, setting the game in a sprawling kingdom in decline and exploring some darker themes like drug addiction, famine, and terrorism.
A great end to the series.