Well from the player's perspective.
Hate:
1. Almost everyone using default ingame graphics.
For games with 3D Illgames/DAZ renders, Yeah i get it, not everyone is a 2D artist. But devs could at least try, everything is better than that soulless default RTP. Also the game at least wouldn't look exactly like any other RPGM game out there.
But what's the excuse for devs who make their porn in 2D, but completely ignore ingame graphics ? If making tilesets and stuff feels too restricting, there is always "parallax mapping".
2. Combat and game balance.
The porn games i played barely had those on an acceptable level. There were no difference in equipment other than the numbers go up, enemies are also had nothing to them, more like same one punching bag with different skin than anything else, those games have no weapon/magic/elemental affinities and things like that to at least make the gameplay not spam same one attack button to win, because nothing in the game is a challenge or require to use your head anyways.
3. Random encounters, especially when they are annoyingly frequent.
On global map is okay, but otherwise i personally think that this mechanic is a remnant of the past and should stay there. Games would be much more enjoyable without them.
What i love about RPGM games as a player ? I don't really know. Everything i would love about a games regardless of engine.
I guess i like RPGM games for almost all of them are low size and and low system requirements, can play that shit on pretty much any hardware that isn't too old.
From Dev's perspective, although I'm not a dev of anything, i played around with RPGM quite a bit.
Love:
1. Easy to get into, coding in not a hard requirement and plenty of plugins.
It really is one of the easiest engines out there for beginner game devs, most of plugins are free, or at least were, i believe most of yanfly ones are now paywalled, but I'm not sure it was long ago. And there is a ton of tutorials on pretty much everything, text and video both.
2. engine provides you with everything to make a minimum viable product.
tilesets, sounds, sprites and other. Although it's both a curse and a blessing, since that's why so many games look exactly the same, but it's still a good thing, they make fine placeholders or just for people who can't do those at all, but still want to make their ideas into existence without having many skills.
Hate:
1. RPGM barely improves throughout the years in terms of what it provides by default, if you can't code, plugins are not really optional, they are a necessity.
Want animated enemies ? Sorry not a feature in our 2015(MV) game engine by default, movement that isn't strictly by the grid ? nope, plugins. Sprite animations with more than 3 frames of animation - plugin, and many other things that imo should be there by default.
That's pretty much all that i could think of now. In conclusion i quite like the engine overall, but really not really exited to seek and play games made in it, since a there is just too much shovelware made on it.