Hi, game looks interesting, quick tip for your team to tackle on, i seen on the video, some of the balls, items, interactive objects are a bit confusing to detect what they do, unless there is a tutorial, or you already know what they are doing so 1st step would be make them more obvious of what they are (an example here would be the elastic in the video, if u would be a regular user, you wouldn't know that should be interacted with, unless u would have went through a tutorial of sorts.)
as for marketing that is more of where, why, when, how long, how much, how often, type of question, and requires time to be put in and perseverance and money in some cases depending on the marketing.
as for user retention is also a bit more complex but requires a team effort, and continuous improvement, simply put you can raise it by giving users a reason to come back, if you pitch to them the game as a "5 minutes game in the waiting room to the dentist" then that's when they will come back... when they have a new appointment with their doctor.
all the above are logical aspects, however logical is not always gonna bring you success, to bring it to success it needs a bit of help from the exploitation of impulses and emotions we as humans have.
if you want to talk some more, leave a email or a form of contact il reach out! :) (the forum doesn't have anymore a private messaging system maybe soon...)