I'm going to start this review with a fact: I suck at this game. I made it onto the leaderboard of dark synth at the basic level, a moment I will cherish forever; I am sure that as rating picks up on the jam I will be pushed right to the bottom - if I wasn't there already. As such, I had more to say about the things that I struggled with, but do know that I tried multiple times and the game itself is very good.
My main struggles were with the control system. I tried both control schemes offered, and they had their own pros and cons. For example, the SDFJKL option was really good for hitting sets of two adjacent notes. However, for more wild note patterns it became confusing which key to press. On the contrary, the QWEIOP system felt more natural with wild notes, but due to the large gap adjacent notes down the middle were confusing to hit. However, as I said I am not skilled at all with this game, and for all I know this could be a very common control scheme that works perfectly well in the hands of more talented players.
I think my brain was sort of leaning towards either an ASDFGH or ASDGHJ control scheme - having all the keys next to each other would make it easier to deal with notes very far apart as you wouldn't have to think about the gap in key locations and for one reason or another my brain kept offsetting my fingers so that I ended up pressing A when I actually wanted to press S. I guess I'm just too used to game controls being aligned right at the edge of the keyboard...
Moving onto the gameplay... showing the next set of notes was appreciated, as it gave me time to prepare my next move. However, as soon as things got more complex I got overwhelmed trying to separate what notes I'd need to hit now and which ones would become important later. Although you lowered the opacity of such notes, the bright colours meant that I could hardly take my eyes off them. That said, it's currently 11PM - roughly the same time I took a hit to both Icicle Fall and Rainbow Wind Chime - so maybe my lack of concentration at this hour did not help with that; I might try again at an earlier time to see if it changes anything.
On the other hand, this game was greatly polished. It had a good selection of songs to play of various difficulty and the UI was well made to not distract you from the main rhythmic focus. Very good work overall, and I suspect that most of the problems I had were simply skill issues.