Some things you should know

Sensimar is a nice hotel with 4+ star facilities and a great staff. But you should be aware that it is not an independent hotel but rather part of a German chain based in Hanover Germany. It is a high volume tourist mill filled with middle aged tourists most of whom are there on package tours. We were there at the end of the season and it was still very full. Breakfast was very crowded, staff asks you for "vouchers" for your other meals, expect to sign away your first born child for a beach towel. The night we ate the buffet dinner, we actually had staff come by in the middle of our dinner and put a little sticker on our sleeve like we were dining in a cheap cafeteria somewhere instead of an elegant resort. And you can forget about getting a glass of water with your dinner. Water is available for breakfast because it is included with your room and cheaper for them to supply bulk water on their dime, but any other time they make you buy bottled water because they can bill you for it. It is too bad that the facilities which are well maintained, the rooms which are beautiful and the staff which is friendly and helpful is marred by the package tourist mentality and policies of hotel management. It could be a really elegant place if they treated their guests graciously as well. If you are looking for a relaxed uncrowded independent experience and personalized treatment, you would be advised to select a smaller more intimate hotel.
The entire Khao Lak area including the Sensimar is currently suffering from salt water intrusion into their aquifer. All of the water, pool, shower, tap is salty. They claim that the water district is working on another well but for now if you are going to Khao Lak, plan on being salty the whole trip.