The seaside villa was spacious, clean and very comfortable. We visited in an off season, but my best guess is, the hotel never feels crowded. Facilities, breakfast and so on are up to 5 star standard. The beach is nice with palms and clean sand. There are many massage places and restaurants around, but I cannot comment on their quality, as we always went out to Fishermen village (10 minutes by taxi) or chaweng beach (15-20 minutes).
What really makes Santiburi memorable for us is the impeccable service. Starting from first day on the staff knew our room number (helpful, if you deposit the key going out and forget the room nr while at it). They followed our pace completely, I.e. allowing for shamelessly extended breakfast times, always patient, helpful and smiling. The nice flower decoration on the bed on my gf 's birthday was nice, but the best part was, that they used her favourite baby gorilla toy, which we brought with us, as it's centrepiece. That's creative - and shows heart.