This is a NGAUC review.
Right off the bat, I hear choirs... which could sound wider, wetter and more humanised. They sound like Vocaloids without any volume changes........
Your instrumentation is good, and not out of place. Your chords and sense of tonality are alright. I can see the vision of what you are trying to compose.
But your mixing and lack of volume control throw the whole thing out of balance.
Now imagine this being performed in a room. You wouldn't have the instruments playing at the same volume with each note, would you? You'd vary each note's volume in the piano roll, to achieve the desired effect. Then, you'd add the necessary reverberation, to make it sound like it's been played in a natural setting. For the choirs in particular, you'd imagine the conductor would instruct them to go loud and soft in some places.
Then come the uses of volume envelopes. Some parts in the song would be soft early on, and then getting progressively louder. Tempo envelopes also could be used to that effect, for instance with the choirs, if you want them to sound solemn.
Mixing is also about recognising the frequencies of each individual instrument, and making sure they do not overlap (so that they don't get 'swallowed'.) For instance, your drums are barely audible, and sometimes other instruments tend to overlap (strings and vocals, etc.). Then this is where equalisation comes in. Give each instrument its best frequency range (for instance, basses about 50Hz, drums about 100 Hz or slightly higher, and so on and so forth) until each can be clearly heard.
I feel painfully for this piece because I can imagine its epicness already. I can hear the final result in my head. But it sounds heavily automated, very much like the humanisation work isn't done.
4/10.