Similar but also different in many ways. One thing is that you can override your pawns' automatic actions with manual things and even queue actions up. Also, no z-levels (unless you use a mod, which actually works decently).

It's not centered around digging/mining, it's mostly collecting resources and building freestanding structures.

I didn't really get into Rimworld until recently after ~100 hours or so in the Steam version of DF, but it has completely sucked me in. Tons of amazing mods as well.

It's really an incredible game with unlimited replayability.