Wordpress Website Registration Page Issue

The biggest concern is the registration process. It is too slow and requires approval according to most of the feedback from everyone. The fact that users have to wait to be approved is going to drive them away – they should have instant access once they sign up. This was unanimously the negative feedback we received about the website so it’s important to make the registration process much easier and instantaneous.
Some users can’t sign in with username, only their email
How can the registration process be made easier? Can we maybe skip having to use an email and just have a username instead?