In my opinion, Ksamil is really nice to visit for a day trip or maybe one or two nights, but that would probably be the maximum for me. I personally wouldn't stay there for a whole week because there isn't enough to do to keep you busy for that long.
If you're not really into partying, Ksamil might not be the place for you if you're looking for a longer stay. Of course, you don't have to party to enjoy Ksamil — I went there myself without partying and still enjoyed it.
Ksamil is very pretty and sits right along the coast. The sunsets are beautiful, and the water is obviously one of the main attractions. However, there isn't a huge amount of things to do, so I would personally recommend it more as a short stop rather than a full-week destination.