The only way to get around the Login/Register page is to use the Facebook User Only option. The login/register page text is completely customizeable through the language files, if you know the language of your visitors. Alternatively, for the Facebook User option, we can help you to change the username to something you'd prefer instead of fb_12345. However, please note that all usernames on your site must be unique, so there needs to be some 'randomness' to the usernames... that way, if two John Jones register, their usernames won't both try to be "John.Jones" or something.
Hope that helps explain, and let us know if you have any suggestions of how you'd like it to work!