Needs some more reverb
I think adding more reverb would make it feel more ambient. Also, I could almost hear this quiet synthy sounding sounding trail following the piano (during the parts without the block chords) - I'm not sure if it's intentional, but I think you can probably play off this more and make it a bit present, and perhaps have it evolve throughout the piece. There were a few awkward pauses after around 3:00 - I think you should make these sound a bit more intentional, even if they were already. Also, I think when you have both the left and right hand playing, the music starts to get clipped, so watch your levels.
Overall, I think this could've been developed a bit more (in spite of being minimal in its roots), and executed with a bit more deliberation.
My new song Liturgic Ceremony is basically this song done up in a much better way. Hopefully you like what I've done with this originally very bland piece.