In 2003 I went back to Turkey for the second time. (First time was in 1995).
This time I stayed on in Içmeler, just down the road from Marmaris. You could go between the two towns by communal taxi rather cheap. Took about 15-20 minutes. You could also walk which I did once along the beach-walk, a very nice walk (provided you don't do it in the middle of the day). Takes about an hour and a half if you don't stop on the way.
The beaches at both Içmeler and Marmaris are long and sandy, but the one in Içmeler is the nicest. Most hotels also have swimmingpools. Generally Içmeler is the quiet place if comparing. Ideal to live in, and then to visit Marmaris when you want more shops, the market and so on.
I enjoyed this stay. Not a place to go back to, but it was nice for a one time stay. It is a bit too touristic for my taste.
BUT, Turkey is a beautiful country with a lot to see, good food, lots of nice carpets to buy.... How nice the place where you stay is depends where you stay.