Depends what you're looking for. Samui is beautiful, loads of things to see and do, warm and clear sea to swim in, lots of fantastic places to eat. The perfect tropical island in many ways. However, Thai nightlife is notorious the world over and over the years Samui has become more and more bland at night. In fact when I was last on Samui, it was positively boring!!
Take what you will from that, but if you're wanting a much more adult theme to your trip then Samui is best passed by.