I'm intrigued by the game, but as someone who is not familiar with old school hex mapping procedures, I'd love to an example turn or two to help me wrap my head around the concept. Has anyone done a sample play blog or a video?

It looks like it is an off-shoot of one of the natural formations results if you are deep enough.

Seems like a nice group of tables for inspiration. Is there a mistake on the note for the Room Content table? It states "Roll 1d3 times on this table + once on the Atmosphere table" I assume it is supposed to be "roll 1d6 3 times..."

I have a question about the solo delve rules. Once you get your dungeon size to 1, you roll for resolution, note the adjustment depending on if you got a clue or a setback. If I understand correctly, from then on you do a resolution check after each new room. So if I get to +4 Setback, it becomes impossible to roll a clue or the objective? Is this intended?

I'm curious, how does this differ from its source material? I played 5e a bit as a player. Is this like a streamlined version?

I actually had the same thing happen in my first layer. I interpreted it as having dug straight up and out of the fort. I then spent resources to patch up the hole it made.