Of all of the Dwarf Fortress inspired games, Gnomoria is without question the farthest along. It manages to bring much of what I loved from DF to a sensible, usable, but still powerful user interface, along with having a unique flavor of its own. in particular, this game has the best crafting system of any builder that I've ever seen, combining flexibility and ease-of-use.
The developer is extremely professional; every bug I have reported has been fixed within a week or two, and he frequently implements awesome suggestions from the forums when they agree with his vision of the game.
If you are not coming from a DF/city builder roguelike background, expect a steep learning curve. Well worth it in my opinion, that is not to say that the game is extremely challenging, in default difficulty the world is forgiving enough that you can probably get by.
The early and mid-game are extremely interesting and fun, but unfortunately late game variety is limited to training yet more powerful soldiers to curb stomp goblins, mining ore to train your blacksmiths and then smelting it down for better quality weapons, and building giant temples or awesome structures. While this is enjoyable, I do feel like a late game should be fleshed out. Given the developer's track record however, I have every confidence this will occur. I don't know how he will do it, but I do know it will be awesome.
Easily worth $20 in current form, $7.99 is a steal.