As an avid rhythm game player myself, as this is pretty much a rhythm game genre, it's very.. mediocore to say the least, let me start with a few positives of the game:
1) Cool music, actually - quite groovy. I'm not kidding. You must have put A LOT of effort into the music (and a lot of the art and pretty much everythigng really), and I actually quite like it. It's not like any full-length song, or anything that will sell records, but for this short length of a jam - it's quite good!
2) Very great art, honestly - everything looks great, you've put lots of creative energy into this and it shows. Only a few games can stand out with this level of fidelity in the art department, and you've done it. The art direction is a bit jenky, but the art assets itself is quite good. I like!!
3) Great UI, including the dialogue, the main menu (CRISP - VERY NICE), the notes during the gameplay, very good!
However, as a game on its own - much to say on the gameplay. I will say I may come from a subjective standpoint, so take my words with a grain of salt. On that note, I am also a rhythm game avid myself so I'd like to offer my 2 cents:
1) Sound design - the notes don't seem to sync well with the music and I feel like I'm mostly just hitting circles at the right time, instead of with the music. I think this has to do with the sound design - you should have a hit sound with when you hit a note at the right time (like a closed hi-hat to start off). Think of games that do this, Osu!, Cytus, Phigros, literally any rhythm games. This gives player feedback when they hit notes and basically tells them, "Hey, nice perfect hit!".
2) Needs a song select - I think this is basically additional feature territory and you might not have the time during the jam to implement this. You could have a song selection to select which songs to play.
3) Very weird control scheme - A,D and < and > keys is a bit jarring to get used to. Especially if they're both on the right side of the screen. To help with the weirdness, maybe you can seperate A,D keys to the left side of the screen and < and > keys to the right side of the screen so they are just like the keyboard.
4) Beatmaps/Level Design in general - I have mentioned this earlier that it feels like the notes don't seem the sync with the music. Especially in normal to hard levels. This is more on the level design perspective - I think you need to find a good rhythm first to place notes on to make a good level. Like a note for each drum kick for one part, then focus on the melody.
5) Weird hit detection, sometimes when I want to hit a note, and missed a notes previously - it instead hits the note behind the note I intend to hit. This creates a lot of inconsistency and I can lose a long string of combo as a result. The note hit detection as a result feels weird and I find myself trying to hit notes earlier than usual - doesn't feel right.
6) Lack of a combo counter - this is what I feel a staple of any rhythm game, to have combos and rack up higher scores when you have higher combos. Rhythms games are perhaps the easiest games for a player to enter the zone (can be argued), and this can be exemplified with a combo meter to tell the player just how smashing they are at the game. It shouldn't have been too hard of a mechanic to implement but I'm a bit sad that it's not in there.
Sorry if it seemed like I'm bashing on your game a lot - I've always loved Rhythm games so much and music in general and I want to see many more music games rise. With your art, your game does have potential but it's unfortunate that it falls short on perhaps the more important aspects which is the gameplay aspect.
With that said, I think you did tremendously on this game - it's clear you've put in so much effort creating all the assets for this game. You just need to work on the pure gameplay element.