The pose and visual weight of the piece works well, having a tail actually balances it quite well, but the red of his costume and the surprise balloon lead the viewers eye to the left, which is good.
However the shading compared to the background is too dark, and maks the characters hard to see. A line work should either be blended into the character, by coloring it, removed entirely, or left solid so the extremities are easily defined.
I like the way you did her right foot, the claw design is quite funky, and works like a little Easter egg to the whole anthro. The overall coloring is good too, although her eye could be a little larger\whiter, to help make it 'op' with happy and squee.
Overall, a very nicely executed and colored piece. As a general comment, just looking at this from a distance makes me wanna open it up and see what you're on about, so congrats on that, it's the main point of any artwork, to draw people in