I thoroughly enjoyed descending Satan's Sphincter with my trusty friend Seth "B" MacFarlane and our random climber aquaintance Joe (probably Swanson).
I was very on edge walking through the dark caves. As another mentioned, however, the mining section was quite tedious. Also,  I made it all the way out of the cave too fast to see the monster (yes, I'm a pro, what about it), but I was really curious as to what it looked like, so maybe the player could have turned around on the rope and caught a glimpse of it quickly?
In a horrifying twist, my irl power shut off partly through the scene in the kitchen, and I did not have the heart to play it all again due to the afformentioned hammering scene. I assume the monster follows you back home and if you get to see it, then I retract my previous critique.

Overall, the game has a lot of charm, some hilarious quirks in the SFX and animation that I didn't mention, and kept me on edge. It's perfect for the theme. Really, I wish I had thought of that. Still less horrifying than real cave diving, though.

"As the man approached the... death... eels ... passage, he.. slipped and fell into a pool of.... six eels. HELLLLLLLPPPPP the man cried out, but it only attracted a .... boulder? which... fell and crushed his spine as the eels kept.... eating him. AAAARRRRGHHHHHHHHH. Right before he could make it to the end, his screaming.... dislodged 4 more boulders which... crushed his lungs and intestines. Unfortunately, 4 days later, the man was pronounced dead, only .... 2 minutes before help arrived on the scene."