Can only really add to what other people have said - beautiful, small boutique hotel. Staff are great - professional, friendly, helpful. Breakfasts were awesome, lots of choice and excellent quality. The cleaners were brilliant, as were the toiletries in the room, this small Greek organic brand that I've since noticed in expensive stores over here. We didn't eat lunch or dinner there as it was quite quiet but apparently it is fantastic. Hire a quad bike or car and visit the many beautiful beaches around the island, we went into town at night on our quad, great fun. It's about a 5 min easy walk, unless you've got mobility issues don't worry about anyone saying it's an arduous walk or stony or hilly... that's rubbish, it's Greece, it's a gorgeous rustic island and you walk up a slight incline into town. There's loads of taxis in Myk town to get you back if you couldn't walk anyway. I would definitely stay here just slightly out of town as opposed to right in the centre as the town is stunning, but very busy, quite big, with small cobbled streets so although there are hotels amongst these streets you get much more peace and quiet - not to mention beautiful pool and view by staying just a tiny walk out of the town centre. The fish resto on the beach opposite Bill & Coo is excellent as was the little rustic tavern in town called Fish Tavern Koynelas. There a LOT of mediocre Greek and Italian restaurants, as well as very good places, to suit diff price ranges, so I would ask the hotel for recommendations or really pick carefully, don't be sucked in somewhere by the bird on the door trying to strong arm you in.
Only negatives really were the rooms were very white so by the time we went, end of season, furniture etc needed a bit of a clean up as white obviously marks and discolours easily, an ipod dock would have been great, the TV was old school and the drinks/food at the hotel are expensive, but excellent - huge selection of fab quality cocktails and wine.
All in all I think if they spruce up the rooms for next season Bill & Coo definitely justifies the price.