I was fortunate enough to buy a reasonably priced Fathom a couple years ago and restore it to my liking.
For me the appeal is as much visual as anything else. The artwork draws my eyes to this game -- even the cabinet art. This is a game I would put on display in the living room if I still had a bachelor pad. I've always liked blues and greens (especially lime green) and this game has those covered.
If I'm being honest on the gameplay it falls somewhere in the middle of good and bad for me. I love inline drops and spinners and Fathom has that covered. It has multi-ball, lively pop bumpers, and reversed inlanes/outlanes to keep things interesting. Building the bonus is a double fun challenge having two colors/goals two work with. One of the biggest negatives for me is a bit of a dead area below the right pop bumper -- I seem to send the ball there all too often.
Fathom will probably be one of the last games I sell from my collection. Not because I think it is such a great player, but because it is a good player and has an aesthetic quality to it that appeals to me. For what its worth I'd also have a restored tractor and possibly a car on display in the living room of my bachelor pad.
I'd honestly have to say the gameplay value may not be worth the high price this game holds, but having an interactive work of art (that I consider this game to be) is.
Other Classic Sterns that I play more often include Nine Ball and Cheetah. I find Paragon to be a good challenge and also like Frontier quite a bit but that has a lot to do with the crickets.