I have had a PA for about a year now. I love it. It's currently a 2ga 3/4" circular barbell. The initial healing is done in about 4 weeks. A good solid healing takes about 3-5 months, at which point you can beat the tar out of it and it won't get sore or irritated. Take it easy till you get to that point. A sore dick is no fun to deal with all day.
It certainly enhances sex and masturbation. I wouldn't say it's a mind blowing difference, but it adds a nice exclamation point.
As far as pain goes, everyone is different, and their experiences are all over the chart. Some don't feel a thing, some cry like baby cuz it hurts so much. My personal experience was it hurt like a bitch for the 2 seconds it took for the needle to go thru, and as soon as it did, no more pain. Your urethra will be kinda irritated for a while tho cuz it's not used to having a chunk of metal rubbing around in it. This lasts for a couple weeks and is more annoyance than anything, and it does go away.
Get it pierced at no smaller than 10ga. If your piercer wants to do a 12 or 14ga, run away. PA's that are that small run a high risk of the cheese cutter effect, essentially cutting it's way out of your dick as it migrates. I was pierced at 10ga, I wish now I would have done it at 8 or 6ga. It would have saved stretching time.
Prepare for bleeding. Some don't bleed at all, but most experience moderate to heavy bleeding. I bled like a stuck pig for an hour, then a couple drops overnight, and nothing the next day. Some people bleed heavily for 2 or 3 days, and lesser amounts for as long as a week. Don't panic when you piss blood for a bit, you bleed on the inside too. Also urinating may be somewhat painful for a couple days. All are normal.
Urination becomes an active sport. There's ways of dealing with it tho. I always think woe is me if I get drunk and forget.
A word of warning about these. They heal extremely well. Given enough time and stretching, these become permanant holes. They will shrink if you remove the barbell, but they will never full close and heal without a doctor or skilled body mod artist assisting it along.
These also like to stretch by themselves. Banging a piercing around in your hand, in a vagina or an asshole, causes the barbell to get yanked around. Genital tissue being what it is, just stretches to deal with the stress. Plan on buying larger gauge barbells as time goes on. That said, larger gauges are more comfortable for most anyways. Things really got fun for me at 4ga.
Last word of warning. If you get one done, you need to be positively certain about your partners not having diseases. This is a perfect entry point for lots of nasties, especially if you are having sex while it is still healing. The unbroken skin is your body's best defense against bacteria and virii, and you just put a hole in that armor.