I stayed at the CocoBay hotel, which is in a bay between Galle and Unawatuna. Lovely hotel - not 5* in the Western sense, but lovely people, great food (the Sri Lankan breakfasts were outstanding) and a great place to relax for a couple of days (note: I'm not a beach person, so the idea of spending more than a couple of days in such a place wouldn't occur).
We visited Unawatuna a couple of times. The beach is rather lovely, and it's great to be able to sit out there to eat and drink at night. It's pretty laid back, but there's a fair bit going on at night. Food was incredibly disappointing - seems to be catering for people who are terrified of flavour.
Galle is a wonderful place, though, and where we spent most of our time!