what
Ok so I hear them loops as always- garageband has a terrible loop library, and anyone who has used and experimented with garageband will know pretty much all of the generic loops. You didn't use too much of the audio loops but I sure as hell recognise the midi loops, don't deny that you used a lot of them. You might have edited a lot of them, but the song is still oh so based around those overly recycled loops. They're not even in harmony- it just sounds terribly off, much like a false singer.
Stop with the loops completely already. Try reproducing some of the melodies yourself at least, if not getting on with what you'd normally do when you've been using a music program this long- composing your ideas as melodies in the sequencer. If you have a midi keyboard, use it, and if you don't, I highly suggest you get yourself one.
As for other stuff- it could need a bit higher volume altogether, drag up the master track/volume (it doesn't ever seem to reach the 0db mark), some more reverb all over the synths would do good. Maybe even a little reverb on the master track (do it subtle if you're gonna do that though). Overall this is nothing new, original or interesting at all in any way. Mostly the same loops (though edited in a minimally original way) going as the main instruments and a bit of additional synths etc that don't do much.