Nice graphics! Sorry for the random immaturity of others from your Tumblr blog for this mobile app. I can tell most of those commenters don't even have artistic talent to began with, let alone any programming knowledge.
When dealing with users like that just take it as a grain of salt. The comments look like they were made by those with no critique or skills and don't hold any validness other than noise feedback. Its common to encounter such things when creating nice apps, so thick skin is a plus.
Professionally, I think the app is just fine. It serves its creative purpose and is a nice side-project. I also love this type of K-art, and yours has a nice digital water-brush like effect to it. Have you considered using Live2D in future?