I really enjoyed playing the game! There aren't many things to gripe about over this title, since it's just that amazing of a game! But there are a few things that I think need to be pointed out, so I shall list them here.
Please keep in mind that this is just my opinion, and it should have no affect on your perspective of the game. There is no such thing as a perfect game. Someone will find something to complain about.
I liked how the game didn't drag on too much, but I feel like it ended too quickly. The game can be completed within about an hour or so, including the fight with Jevil, which doesn't seem so great when you look into it.
I like most of the music in this game more than Undertale's soundtrack, But I feel like there was some times where the music kind of got old a little too fast. For example, the fighting music could've been mixed up just a tad more.
Lastly, I think that there should've been more bosses. Lancer, Susie, King, Jevil, The giant Checker thing... I feel like there could've been one or two more. For instance, when you would go to find keys to unlock Jevil's fight, there should've been someone blocking you from getting that key. And to obtain it, maybe you should've been assigned a task or you had to fight them.
That's pretty much all of the complaints that I have for this good game title. If these problems were fixed, then I would give it a five stars. Although I know that isn't going to happen, I may change my review just in case. Thanks for reading this, and I hope you have a wonderful rest of your day.