Good job. Nice atmosphere & mood.
The rest of my post is mostly critical, but that’s because i’m generally more inclined to write critique. Also, i’m only writing in detail about visuals. Hopefully i’m not doing too much nitpicking and my feedback may be useful.
First watch impressions (roughly in order of appearance): animation is “cheap”, but smart enough to make that not very irritating; and amount of animation makes it interesting to watch. Zooming is jerky (seems to be common with Synfig, i think). Next, the contrast between animation and real world video - the style is completely different (more on that later) and the first cut back to real world is without transition. But then the parallel between the two worlds is caught and that is of course cool. The sync moment at ~1:54 seems to be too short to really sink in, but good enough to be noticed. Finally, i notice that the animation is in one place, but at different times, and the real world is in more different places, but mostly with the same light & time of year.
And now for some deeper analysis.
As i mentioned, the contrast between the animation & real world is a bit too much and i think there might be a way to reconcile the two without too much additional work. Just making transitions longer and including common coloring (not sure how it’s technically called, but can be achieved by putting a semi-transparent color clip that fades in&out around the transition) would improve things a little bit. Of course, having similar (or alternatively nicely contrasting) geometry of the transition frames would also help.
Another thing is color balance in animation regardless rl video. Might be my personal preference, but i liked night & winter parts more than the rest. Palette of too saturated, contrasting colors (and most importantly not related in any pleasant way) doesn’t look especially good.
And finally, some nitpicks. Bear sprite changes at ~1:19 looks out of place. Maybe it would look better without fade, or perhaps with timeskip (like ~3:16) effect in place of pseudo-smooth transition. Multi-way zooms like at ~0:40-0:51 might look better without stops (perhaps using path following can be help). Reflection in the water is doing more harm than good: it is not clear enough what it is at first sight and on second sight it isn’t that accurate.