Nelson took the words right out of my mouth. Were you to replace all instances of Pokemon with substitutions from some original IP, this game could stand all on its own, and could've probably done quite well for itself as a GBA era game were it commercially released.
Given the preamble, I went into this game expecting it to be like a turn-based, party-centric, RPG, a lot like the JRPG's of old. I quite like the idea of pitting your Pokemon teams against a single beefed-up boss-mon, like Nintendo tried to do with the Raid Battle mechanic in their newer games. The combat system that the devs implemented is very robust, but like RB says, it's quite involved, so be sure to read the battle notes. I also like how progression isn't tied to XP from winning battles, but rather the rewards from the defeated mons in the form of Moves and Abilities which they drop which can then be "equipped" to your mons. It's cool that the progression of your team is tied to which Pokemon you defeat. The problem is, after defeating the boss and completing the run (called "stories"), you are sent back to the hub, and your team is reset and randomized for the next story you undertake.
Furthermore, a lot of what you know about traditional Pokemon battle mechanics goes right out the window. Play Pokemon long enough, and you get a really good feel of what attacks should deal how much damage to an opponent, or what attacks will outright OHKO a foe. That is surely not the case in Record Keepers. Often times I found myself hitting or being hit by super effective 100+ BP attacks, only to have the health bar depleted by amounts far less than expected. Funnily enough, I found the most success against the first boss, Xerneas, by soloing it with my Florges who picked up Toxic from a defeated Salazzle. It was a lengthy but safe battle as the Toxic damage chipped away one health bar after another, all from the safety of stacking Calm Minds, on Grassy Terrain, and healing from Xerneas' Circle of Life Ability.
But beyond that, the graphics of this hack are utterly gorgeous. It sort of feels like an adaptation of Hisuian aesthetics, and really makes me wish for a hack set in ancient times with a story uncovering myths and legends of the past. Hoping the graphics artists lend their talents to a more traditional rom hack, so I can experience them without the growing pains of a rogue-like. It's clear a great deal of talent has gone into this hack. Give it a try if you are willing to endure the piecemeal gameplay in order to discover what seems to be quite the in depth story from a lore perspective!