Melody's voice can be very hit or miss for me.
When she is in the pocket and produced well, she provides a pleasant warm brightness.
Her voice can be the stabilizer and it works really well on a song like m-flo's Miss You, where things could easily be TOO chaotic. But it all gels perfectly.
Whereas a lot of her solo material, especially lovin U, is just too much of the same energy in the vocals, in the production, in the arrangement, that it just becomes very plain. And then the emotional resonance simply isn't there--the delivery is very one note. So when a key change happens, it feels more like they didn't know where else to take the song.
Ultimately, it's a 5 because it's an average and listenable song.
I wouldn't choose it to listen to but it certainly isn't terrible.
This song specifically is very background music for a first date montage.