Great hotel, clean, very good service. Nice large rooms, well-equipped. Comfortable bed/pillows, satellite TV channels, nice swimming pools, great gym and steam room (all free to use).
Squash court not in great condition - uneven floor and very slippery, but OK for beginners - rackets and balls are free to borrow.
Breakfast buffet spread is very good - LOADS of variety.
MAJOR problem with this hotel's breakfast is the small area in which it is served. It's served from 6-11am, and most days we went around 9:30-10:00 because any time after 8am it's hard to find a table - we gave up twice and went back to our room and waited until later.
The food in the restaurants is good, but very pricey......recommend don't bother paying the exorbitant prices for any desserts - they're not worth it!
Apart from those 2 things, no other complaints - the service of the hotel staff was exceptional - we've stayed in many hotels in Thailand over the 10 years we've lived here, and would say the service/friendliness of the staff at Mai Samui surpasses most other hotels.
This is NOT a hotel to stay at if you want a nice sandy beach, and if you want to be able to swim in the sea/ocean. You can only swim in the ocean at high tide, and even then you only get waste deep in water, and there's rocks all over the seafloor - not very nice for swimming in. But the hotel swimming pool is massive and very nice for swimming.