It was great. Sunny Beach is far cheaper than any other beach I had been to and just as nice. During the summer (or late May when I went) it is more of a college (Spring Break) style place with a lot of German and British 20's or so roaming around. I didn't mind that at all actually and made pub hoping fun. Nessebar is also pretty nice to venture to for the day. But nothing beats the price of the hotels. I got mine on the 11th floor over looking the Black Sea for $85 (US) total for 2 nights on a weekend at the end of May. So put that with the cost of food and beer which is very cheap in comparison to most of Europe, then it makes this place a fun place to go see.
I also noticed a number of places doing day tours to Istanbul as well if you were interested in spending more time at Sunny Beach.
We drove through Golden Sands to the North and it seems more of a family oriented beach location than Sunny Beach is. I'm sure it is just as nice as it looked out the window.
Bulgaria is also really green. Probably one of the greenest looking nations I've seen out a bus window...