Anyone have any experiences (good or bad) with dive schools / operators on Koh Samui (ahh, the interchangeability of 'in' and 'on' when referring to an island - discuss.) ?

We're going in September, and my other half will need to finish her PADI OW course (4 teaching dives), while I would like to do something a little more interesting.
Just re-read that, and realised that it might seem a little dodgy, given Thailand's reputation - I mean interesting in a sub-aquatic sense

Many thanks in advance
Stewie