Hedonism — the claim that pleasure is the only ultimate good and pain the only ultimate bad — has a worse reputation than it deserves. Its serious advocates weren't decadent libertines. Epicurus, the founding figure, lived simply in a garden with friends, ate mostly bread and water, and thought the most reliable pleasures were the absence of pain, anxiety, and want.
The interesting hedonist move is to keep asking "good for what?" until you hit something self-justifying. Most things we value (money, fame, achievement) are valuable instrumentally — they lead to states we like. The hedonist insists that what makes any of this valuable in the end is the experience it produces. Even the satisfaction of knowing you've done good is, ultimately, a kind of pleasure (a refined one, but still).
Nozick's "experience machine" thought experiment hit hedonism hard. Imagine a machine that could give you any pleasurable experience you wanted, indistinguishable from real life, for the rest of your life — would you plug in? Most people say no. They want to actually accomplish things, actually be in relationships, actually know reality. If pleasure were the only good, plugging in would be the obvious choice. The fact that most of us refuse suggests pleasure isn't the only thing we value — though figuring out what else IS valued, and why, turns out to be much harder than the hedonist made it look.