The initial/main melody is very compelling, also its timbre, it's a shame it gets obscured for most of the piece, in my opinion
Also I think the drum-loop from 1:04 to 3:34 is too short/repetitive, and gets boring by the later half despite the added elements, though the part when it slows down is very good.
The ending part is very very good, my favorite part of the piece in fact. Though I think it could've been a little better if the main melody could be heard more clearly, on top of what I think is a delay, rather than drowning on it, or perhaps just too low on the mix, either way. Also that heartbeat kick works really well in it.