Being taken away from the pains and trials of this world as you create your own characters and situation. Writing can be amazing therapy.
Seeing your work in print or on the web and getting good feedback (good in terms of useful criticism and, yes, some praise is nice but beware the flatterer. Vanity presses always flatter).
Getting the first draft down and then improving it by cutting out what’s not needed and knowing the story really is much better. I get a lot of satisfaction out of that and it improves the chances of publication no end!
Enjoying well written how-to-write books as I learn a lot from all of them! I particularly love reading interviews with other authors as they explain what works for them. It’s encouraging when you realise you’re finding the same things work for you.
Enjoying the subtle phrase, oblique references (Terry Pratchett’s especially good at these) and hopefully getting to write some too! It’s a bit like finally cracking the cryptic crossword when you come up with good oblique references of your own that you know others who read reasonably well will get.