Alpha 8 still needs a fair bit of work, if only because it tends to persistently throw out game-ending bugs around Day 8.
The surprising thing looking at the Dev Roadmap right now is how much of the core game they’ve actually completed. I mean, the game is still pretty bare-bones, but the bones are mostly there; the only really major major game element on that roadmap that isn’t at least partly implemented is water. Everything else (seasons, advanced classes, more varied types of monsters and enemies, etc) all seem more like matters of adding additional content rather than developing new game systems. Even multiple-story buildings are technically in game right now, they’re just awkward and difficult to actually build; that’s more an interface/ui issue than an engine one.
I suspect the biggest hurdle from here on out actually isn’t on that roadmap – simple memory issues. Even with Dwarf Fortress, most people tended to abandon their forts along about the time they hit 100+ settlers just because of memory and processor speed problems, and that was with ASCII graphics! Of course, the Radiant guys are professional programmers, whereas Toady is self-taught, so hopefully they can be a little more efficient.