It's clear a lot of effort went into this, and I encourage everyone involved to keep creating, because I think it shows a lot of zeal and potential. In terms of effort and passion, I give it five stars.
That said, I have infinitely more to say as an assessing teacher than I do as a praising voice. I want to be clear I mean this all in the most encouraging and supportive voice possible. This is not negativity, it is encouragement for improvement.
-Do not use multiple line weights in one sprite. FNF has a very distinct line weight in its art, and its fairly uniform. Frankly you shouldn't mix multiple highly different line weights in any art, but especially not in an FNF sprite, because it's highly noticeable.
-I don't know if its the engine rebuild or the fact that its in browser, but the timing feels very off on a lot of things. Notes frequently don't feel like they line up with the charting, and the animations don't feel sync'd at all, eliminating their role as a metronome for the player. Overall, the gamefeel is not very good. Considering the game doesn't seem to lag at all, it might just be the charting itself that's off from the music, which is a different problem.
-The music is quite nice, but the mixing is a little weird. BF and Isaac both get washed out by the instrumentation a little.
-The mechanic in the second song is a little confusing. Do curses only show up when I miss notes? If so, what's the point? If a player is already losing, then making them lose faster isn't very interesting. And if a player is already unchallenged, then having their reward be to remain unchallenged is odd. I barely interacted with the mechanic because I just didn't miss any notes.
-I have no feedback for the third song, because someone put an instant kill mechanic in it. This may be my personal preference, but I believe that you should not do this ever. It's just bad. A great many FNF mods confuse instant kills for difficulty, and difficulty for quality, but both are fallacious. A good mod lives or dies on its music, and if you feel the need to make it difficult above all else, it actively hinders the ability to enjoy the music.
Even good mods like VS imposter fall victim to the idea that instant kills are anything but tedious. Design better.
The instant kill in question is poorly communicated, to the point where I had no idea what happened the first time it got me. The second time, I worked out the mechanic... and had absolutely no desire to entertain it further. It was an instant slam into the sandwich point for me. If a mechanic is annoying, confusing, or tedious to grapple with, most players won't bother.
Overall, a great showing of teamwork, effort, and potential, but one that leaves me looking forward to the next week more than leaving me impressed with the current one. I really hope everyone involved keeps working hard, because its clear you're all capable of really great stuff! I wouldn't have written all this if I didn't think so.