Tattoo pain seems to vary a LOT from person to person. I've talked to people who found it hurt more than they expected and the opposite
I think it's biological (your pain tolerance) and your ability to relax. Relaxing is super important.
It's never been too bad for me. I feel that "a cat scratch" is about right. It's like stinging from soap in a cut, but with pressure. I relax very well, to the point where I'm in a mediation/half-sleep state.
Also, if you have a large tattoo, your body starts to give up on numbing the pain usually 3-4 hours in, so it will start to hurt more - and you might want to break the tattoo up into multiple sessions.
I only have my earlobes pierced. I want inner conch punches, but that will be a while in the future.
I have four tattoos and an appointment for the fifth.
My first was a heart, then a bird on each arm (Beardsley peacock and Picasso owl), and a big awesome combination of two Louis Wain cats.
I'm not sure if they're addicting. I think it depends on what you want. I've always liked tattoos and lots of tattoos and artwork. Some people are happy with just one. Some people hate it so much and regret it (I just say that because it's a possibility).