I kinda get the feeling that the high frequencies are somehow missing in the song. Also, when she's singing with the melody the voice is weak compared to the "power" and "volume" of the synth.

Also, beware of successful pop song structures (which I don't notice on this song), I think they (should also) apply to remixes as well.
Basically here it's a Long intro - Melody - breakdown - breakdown&vocals + Melody&vocals - short outro... that configuration is a bit unusual.

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