Hi Rorosengarten,
Congratulations on making your first appointment. I know how terrifying that can be. You'll probably be a big ball of nerves between now and the appointment, but once you're through with it, you'll be so proud of yourself.
You should expect the first appointment to be a visual exam and some x-rays. I'd recommend writing down some of your fears, along with your story, to share with the dentist. Some people send a mail or email in advance, others bring it with them. It's easy to lose yourself while you're trying to face the dentist, so it helps to have some things written down. Anyway, the dentist will want to look in your mouth, and will probably use a mirror, but will be very gentle and won't poke or touch anything that looks like it might hurt. He should explain what he's doing and probably ask permission before doing anything. He'll also want to get some x-rays, which aren't fun, but aren't painful. If you have any pain biting down, that would prevent you from holding the x-ray bit in your mouth, tell him or include it in your story.
That should be everything that actually happens with your mouth. From the visual exam and the x-rays, your dentist will go over what treatment is needed with you. If you have any questions or concerns, you can bring these up here. The important thing is to develop a bit of a relationship with the dentist, gain some trust in him, and learn what you need to have done.
You should not expect to be shamed or judged or lectured. Most dentists know that it's hard for a patient to come in after so long away, and will avoid being mean, and help you just focus on what they can do to restore your smile. If your dentist is mean or lectures you, you can always thank him for his time, and find another dentist.
The important thing you should pick up, from the dentist's behavior and from your conversation, is that you are in control. You can schedule an appointment to start getting work done right away, or you can go home and think about it and call back when/if you're ready. You can try to fix everything, or you can focus on certain teeth or certain problems, and address them as your time and tolerance (and money) allow. Your dentist should let you know if anything is an immediate concern, but even so, it's your call whether to start work on it or not. If you need more or less explanation, the dentist should be happy to provide it. Although they have a job to do, good dentists are always focused on keeping your as comfortable and out of pain as possible.
Most people are surprised, after so long away, at how little work they end up needing. There's no way to tell what your diagnosis will be, but even if it's a lot of work, just focus on fixing what you can, and a little at a time, you'll be moving back toward a healthy smile.
I think you'll be surprised at how easy the first visit is, and how little judging or scolding there is.
Good luck, and keep us posted!