Cassette Beasts

So first off, related to above, I think the monster designs are far above the usual "Pokemon clone" in quality. A lot of these games can descend into "cute/cool animal + X element" but I think the devs wisely avoided falling into that trap and there are just a ton of really cool monsters in the game that aren't derivative of other games.

The second is the combat system. An AP system lets you decide if you want to pump out max damage each turn or use weaker attacks and shoot off bigger ones later. Where I think it really shines is in Passive moves though, as you can set up moves that will automatically trigger whenever you do something. I managed to get one set of moves that always crits on type advantage and another that will auto-attack on a critical hit that together make an infinite damage combo if I have type advantage. Pair that with a monster that can change the foe's type and I can obliterate almost anything in the game.

Lastly the I think this game does a really good job with boss encounters. You can fight rule-breaking eldritch monstrosities, fused monsters, and actually competent rival humans with unique teams and strategies and all of them have different ways you need to battle them.

Oh yeah, and the music rocks. Plus when you're battling, if you fuse with your partner the song gains vocals. It's a bunch of cool little touches that make the game special like that.