I think they went overboard a little in winking at the audience that they have this huge selection of characters to draw on over the season(s). Like the pilot had Catwoman, Batman, Penguin, Riddler, Poison Ivy and possibly others I missed. But they are probably all background/secondary characters, at least for a while, and they seem to be using them to show how Gotham created its heroes and villains - like Poison Ivy:
Its also worth noting that Arrow did basically the same thing and is near universally considered a success and actually a really solid show. Introduce characters fast then push them to the background is a decent formula.