I experience a similar disappointment a year ago, but I learned and used it as a resume builder to land a job in a gaming company. Now eight months later, I have worked on several projects, met a lot of other developers and collaborated with two of them over weekends to release a somewhat successful game. The best thing you can do is get into the industry full-time. They can provide a lot of opportunities to learn and grow as a developer.
First, will a new project make a difference? If the problems of artwork and marketing - especially the latter - remain unsolved. ( I'm in the same condition and I won't draft a second app.) Second, people say ads would be a lot of money. But if you can only get $1 back for $100 spent, what's the difference if you spend $1,000,000 ? Only to get 10,000 back? Anyone with experiences? Perhaps no one replied here has the real experience of struggling out in the same condition. Provided that, all the suggestions could be misleading, you have to think for yourself. Anyway, good luck.
I've made 14 games, but I still haven't found a good way to reach out to a wider audience. this business is extremely hard ...
Good advice and comments! This is a good reply, thanks! If its any consolation OP, I am also experiencing something similar in terms of download numbers so you're not alone! But at least you tried and can keep on trying and improving yourself with your games and apps and building up the experience. Good luck (i know, for one, I will need it for myself for sure!)