I have a IMDN, no AFMr. But spent a full weekend playing a AFMr a couple of weeks ago. LOVED IT. And was tempted to get one. But after a hundred plays, I prefer IMDN. The modes, and goals in IMDN are truly fun and have more depth. But AFMr is just a fun pin, with a superior light show. And I felt it was built better.
For the music - well it's good pinball music. Like others I messed with music attenuation, so it's more background music. It's been good. The callouts are awesome, and he taunts you quite a bit.
Some of the modes in IMDN are TOUGH. Flight if Icarus is pretty much a Keith Elwin mode, that rewards you for ramp combos. I've hit a 4-way combo once in the mode. Takes a lot of awareness and focus to not drain while shooting alternating ramps. It's stuff like this that makes the game so entertaining. Stacking multi-balls in some of the single ball modes. Lighting revive. Loop jackpots are a hoot. There is just so much to do there.
I convinced myself to overlook the IMDN theme, because it's really a "Eddie Monster" theme. And the IRL band doesn't appear on it.
My 2c.