Shiralea is definitely a flashpacker hostel. It's designed and run by westerners, and has bamboo bungalows, bamboo bar with plenty of Western food, chlorinated swimming pool. Loud music is played in the bar, which can be heard everywhere. Haad Yao beach is a 3 minute walk, and has restaurants and bars along it, with tables on the sand.
When I stayed at Shiralea there was a Contiki tour group. They painted themselves in neon colours and danced under a blacklight in the bar. One guy rang the bell and bought everyone a shot. Depending who you are, this sort of thing is a major pro or con. I didn't mind, and enjoyed the spectacle. The music played until 1am. I was in bed around midnight, and used earplugs.
Overall it's the best backpacker hostel I've seen.
Low water pressure around 7am in the morning, which meant the water instant heater on the wall wouldn't stay on. Then the water went off. Granted I only stayed one night. No idea what happened.