Having some people review events listed on my host profile page, I got feedback that it was confusing that a pay event had buttons to register for "Series" or "Drop-in", but there was no button for the free event (I would assume probably also not for a single event that required payment). The user complained that it was confusing looking for a button to click on to register for the free event and it was not clear that you needed to click anywhere on the event to go to registration.
I would propose that for consistency, all events have a button to register. Probably 3 versions: "Register" for single events that require payment or are free, and the current "Drop-in" and "Series" buttons
Since I just noticed that whatever button you click just takes you to the specific event registration page and you have to click on Event Series or Drop in again, just have one button for all events that says Registration Page then they can select the appropriate option there.