Really the whole process is fun for me. From thinking about what ingredients to buy. Sometimes even buying them since I see friends at bulk buy pickups. Coming up with recipes - and sometimes doing something off the wall.
Brewdays are usually kind of a Zen thing. The flow of usually kegging, prepping, and brewing at the same time is satisfying.
Sharing brews of course is another great part of it. I've met a lot of people over the years that remain friends I never would have met otherwise.
And of course I get to drink the beer I brew - that's nice. And as Ken says, time excepted, it can be cheaper. And since almost all my equipment is DIY it really wasn't all that expensive.
But, cleaning still sucks........