While I own Avernum, Avadon, and Nethergate on Steam, I couldn't really get into them because of the slanted, diamond-grid perspective. For whatever reason, the top-down, square-grid perspective of QW allows my brain to parse the environment better and faster, and so I've been able to stick with it long enough to be hooked by the scenario, plot, stories, and quests.
Combat/fort upgrades are just a means to an end: I'm in it to discover where this world has been and where I can lead it to.