Really great game, especially for a solo developer doing art and music. The graphics are nice and clean and the game controlled really well. I was surprised by how well it worked, especially for a browser game.
Design: The core gameplay loop was fun, but needed a few small tweaks to really shine. Some attacks had great impact, like the bazooka, but I would have pushed it further. Screen shake and more sound effects for every hit would give the game extra juice.
Graphics: Wonderful work here. Only thing that might be needed is to hide the trees in front of the camera, which got in the way at times.
Theme: I wish you would have pushed the theme further. The risk/reward mechanic always made me want to not take the risk and just protect the dog. The only times I choose not to were when I was forcing myself to have fun. I agree with the other comment that breaks would have been nice.