Great
It was a fairly touching piece in my opinion. The dark colors with the very smooth animation made it fit the music perfectly. It doesn't really pull you down as much as would be expected with an opening like such. But instead it kinda just reminiscences on the happy times spent with the cat, and the things the cat would do as part of the main characters habits. In the end it was fairly magnificent with the tree and toy that was used as a friend for the cat. It wasn't really as depressing as some others have claimed it to be.
But anyway, very nice job.:
Sound: 8/10
graphics: 9/10
Creativity: 7/10
Animation: 8/10
Overall: 8/10
Nice work, hope to see more, do improve a little bit, in this particular piece i cannot recommend much, but find flaws on your own so you can become a greater artist :).