You sure like flashes don't you? XD Anyway, the sync in this was done really well, but I think you overdid it a little. Especially in the beginning, when all you hear is this piano? sound and quiet singing the video moves rapidly and flashes on every note of the piano-thing when the singing suggest it should actually be a slow part. In the middle part some of the flashes were a bit too strong in my opinion, but since the beats are a lot stronger here the pacing felt a lot better. Also, between 0:46-:048 you go back-forward-back-forward, this kills the flow a bit. (I suggest watching http://www.youtube.com/watch?v=Cu6h0MDnF6w
, I wouldn't have been able to tell what exactly felt off about that part if I hadn't seen it). The last part is where, to me at least, the video fits the music best. Flashes seem (not sure if they are) a bit weaker than in the middle, transitions feel better because the scenes are more similar. That's the way to go! One last thing: there were white borders around the whole vid. I assume this was intentional but I don't really understand why. It's like you made a screen... in a screen.
Either way, don't let this wall of text discourage you. You definitely have skills, they just need some finetuning.
P.S.: Completely unrelated note but I'm pretty sure the word "collab" is used for having two editors on one video, not multiple sources.