I have found it too hot in Sunny beach to be able to function. It is not the most interesting place to explore, because of all the nasty concrete hotels. The central area by the beach seems quite small.
The 5 minutes I managed to stay on the beach suggested that the beach was nice and clean. Unfortunately, it was full of people on the beach which freaked me out and I had to get off and get on the concrete pavement.
After watching the TV program: "What stays in Sunny Beach", which showed a bunch of young people getting trashed and shagging, I was ready for some hedonism. But the place seemed full of families and old people soaking up the sun. Perhaps I should have stayed out past 11:00 to see the wild side, but I was tired.
All the Bulgarians were super friendly.