Firstly i have to tell you how much i love the outlines thin on the inside and thick on the outside. secondly the shading technique you had used on this is great, but also it coulda been a little bit smoother on the transition of each color but on the other hand it suits this drawing.
The background is just amazing, simplistic but amazing also it makes Miss Ditzy Doo/Derpy Doo and Doctor stand out and forces the eye sight to focus on them instead of the wool drawing as most people would do (at least that's my opinion).
From the facial expressions as usual Miss Doo is happy as hey because of this situation,but on the other hand she seems quite pleased like she planned this moment for long time. The doctors face just cracks me up every time i look at it, its like he is in a super extraneous position but he quite enjoyed it in a way, like he was waiting for this moment for a long time but this seems like a big surprise for him that she had made this move.
P.S.Sorry if some of this doesn't make sense, English is not my first language. also i love this drawing <3