I'll type up something more comprehensive later this week, but for now, I just wanted to say that our user impressions of the game's difficulty and its curve across zones might be biased, since we're totally in the dark with respect to the final zone, facing The Thing Below.
Whether that final stage hits like a sledgehammer or feather-duster remains to be seen (or rather, felt). Lotsa roguelikes require the player keep in mind that final skill check, as it were. This usually means deft tactical maneuvering on the player's part towards some end-game, end-boss viable build (*ahem FTL*).
Final Boss aside, though, I'd say the difficulty curve feels pretty good for a one-setting-fits-all build. Lotsa small interactions and cues to learn and streamline into a best-practices mindset. Not sure how much room there is for individual experimentation without just feeling suboptimal.
I tend to hit a sweet spot, usually in the middle of the second area, during which my confidence in the that runthrough's odds surges as I feel the build coming together.
Again, I'll pen a longer and more specific, itemized account of my experience so far later on.