Dopamine is strong but subtle, I believe. You don't get the sudden rush you might get from an illegal drug. I guess it is more like the satisfaction of the first sip from an alcoholic drink; you don't get drunk immediately, but you feel happier once you've taken that first gulp. And like alcohol, your brain makes you crave it, without you really knowing.
I recall my last few porn sessions (5 months ago). I thought it was a simple matter of wanting to do something which was fun/interesting/exciting, just the same as the feeling you get wanting to go out to socialise, or go to see a live band. But porn is free and available in your own home; it is as bad as the biscuit tin for a dieter - always there to tempt you. So the feeling beforehand was (apparently) a simple interest, no wild craving or feeling of madness (so I thought). I thought I was in control, and choosing to do something intentionally.
During the browsing session, I would lose track of time, go into a sort of trance. It all felt very fluid and immersive. I wouldn't have said I was experiencing massive powerful happiness/pleasure, like I imagine illegal drugs give....I would have just used words like contentment - a nice level of happiness - and arousal. I was enjoying myself, absorbed, excited. But if questioned I might have realised this wasnt the same ecstasy I get from live music, or from a great moment performing my favourite sport.
That is why I say dopamine is subtle - both before and during the hit. You want it badly, but you think you are consciously choosing to go and get some. Then when the dopamine starts flowing, you are so absorbed/immersed you don't notice it hitting like an external drug (alcohol/tobacco/pot/coke etc) does. Lots of little hits keep you topped up, in the zone.
The second you finish - WHAM! The guilt hits. It is like you're suddenly dumped back into real life, and realise what you've done, as if you were not aware previously! Where has all that time gone? It is so stupid.
It is like an would-be-dieter gobbling a cake. I get enough pleasure (and guilt) from food to know what this feels like. You can want that sugar so badly you dont think rationally.....MUNCH.....and afterwards you feel that sudden 'back in the room' feeling, and cant even remember if you took the time to savour the taste properly.
Your brain releases dopamine when you eat nice food too, so I wonder if there are lots of cross-overs between these two problems, porn and unhealthy eating. We get so used to eating food we almost dont notice the drug hitting.