I don't play a huge amount of RPGM games. Especially Japanese ones, but I can give you some input what it takes to get someone like me interested.
Interesting artwork is the biggest one obviously, and it's partially why I don't go for a lot of Japanese RPGM games(that and seemingly 99% of them only having female protagonist). They all basically look the same to me. One thing that stops me from a lot of games is the tiny resolution of both the game and it's artwork. 720p is the minimum for me. Unique world assets is another big plus, using the default tile set isn't a deal breaker, but it will make me more likely to scroll past it and forget about it.
Second is gameplay. I don't want an ordinary JRPG but just with adult content. While some combat is okay, I've never been a fan of the turn based combat in most JRPGs. They need to either have a decent gimmick like Persona, or have a great presentation like some of the FF games. RPGM games tend to have neither so I just get bored super quickly. I'd rather just have a combatless sandbox game than budget Final Fantasy with the occasional porn image. Unique gameplay/sandbox features is what get's me excited. For example I tried out "The Imperial Gatekeeper" despite not being a fan of the art because the gameplay sounded intriguing(granted it was far to grindy for my taste), I also played a fair amount of Violated Heroine back in the day because it had simple action combat.
For reference, on the top of my head the ones I've enjoyed have been:
Farmer's Dreams, great presentation and really interesting, the main issue I never played more of it was RPGM itself making the game play really awkwardly, and the thing was just laggy. Should have been a Unity game or something.
Lust Epidemic, I kind of hated the world art at first, but the uniqueness of it pulled me in. As a fan of Resident Evil I rather enjoyed the atmosphere and puzzle gameplay and it really ended up growing on me.
Peasant's Quest, It was just a decent sandbox experience. Granted it was fairly early in development last I played it and needed better paced erotic content, and I think some of the grinding got pretty tedious.
Town of Passion, the clean and simple art drew me in, all in all it was just a fairly pleasant experience, not anywhere near my favorite game or anything, but I enjoyed my time with it.
The Imperial Gatekeeper, unique gimmick. Was kind of fun but pretty got pretty samey after a while and the actual porn was pretty low quality.
Violated Heroine, just a classic. The translation issues mixed with some of the insanely complex and arcane nature of the quests were the big issues for me, that and the low quality art, but that's mainly due to it's age.