Despite my earlier comment about Dwarf Fortress, I've played it for a while and immensely enjoyed discovering the things you can do. I can see why people find it unplayable though; it requires a lot of patience to learn the controls, and some of the gameplay elements are extremely hard to figure out (building an indoor water supply and a lasting food stockpile to survive the first winter, for starters). Once you get past survival, it's a very rewarding game to play.
Plus, DF is a software engineering masterpiece. JADE has the same potential, and at least Biskup shows a similar persistence in developing it. JADE is supposed to provide a lot more complexity than ADOM, but I sincerely hope the learning curve isn't going to be as steep as DF's (or even Incursion's). Adams took the risk of scaring away thousands of potential players when he created a unique work of bizarre genius. JADE however is a game in a tradition of roguelike RPGs, and if it is to meet the expectations of ADOM fanatics, it can't afford to do the same.