(this ended up becoming a bit rambly but hopefully there's something useful dx)
Composition: High marks all around. Especially the melody starting at around 1:20, while containing only half notes, caught my attention quite effectively. The drum patterns are also nice, if not a bit simple. Composition is definitely the strongest suit of this song.
Structure: Likewise, good stuff. Good usage of percussions in transitions such as around 1:06 and 1:19. The song doesn’t linger on any single moment for too long, and there’s a good sense of direction, and there’s plenty of contrast between the sections, so the listener doesn’t get tired.
Instrumentation: I can see that it’s meant to be a duet, so I won’t complain about the sparseness of the instrumentation :p However, in these cases the need for the instruments to pull their entire weight becomes even more apparent, and I think here they are slacking off a bit. While as mentioned the things that are played are quite good, the things that are playing could use some refinement.
For example, everything sounds a bit “dry”, as in, the elements don’t seem to have much reverb in them. Especially for a song this sparse, having enough reverb to provide a roomier sound can be very beneficial. And this indeed also suffers from lack of humanization, but because that was comprehensively talked about in the NGMT reviews, I’ll skip over this. Percussions are OK, but the clap especially could punch through the mix a better, as of now it falls a bit too much into the background at some points.
Mixing: Mixing is OK here, nothing sounds like it clashes with the other elements, though this is of course helped by the light instrumentation. The stereo field could maybe be used a bit more though, meaning that some elements could be panned to the left or right more. For example, if you had 2 pianos (which it sounds like), you could pan the other a bit to the left, and the other to the right. Same with the cymbals, they could be panned around a bit, but I’m not sure if that’s possible in MuseScore.
However, one definite shortcoming is that I do think there’s a lack of low-end frequencies, and I think that harms the otherwise upbeat and bouncy vibe this song has. I’d ensure that the low notes of the piano are playing loudly enough, and maybe fiddle with equalization if that’s and option. Honestly, introducing a third instrument and having some sort of dedicated bass could probably help with that as well.
But yeah, overall, a very good song you got here, especially when it comes to the arrangement. Some improvements are to be found in mixing and especially sound design / instrumentation, but you are standing on a very strong basis already :) Lastly, I do think I should mention that “acoustic” music is not my strength, so take the things I have to say with a healthy dose of scepticism :p
I’ll also link this comprehensive orchestral mixing tips news post made by Everratic: https://everratic.newgrounds.com/news/post/1329330. Granted, much of it is useful only for higher-end stuff (doubt you have access to mic positions :p), but it still might give you some ideas.
ObeseChihuahua1 
