We've been coming to Unawatuna for years, so we've seen guest houses come and go. But Lucky (and his wife, Pemma) keep the same basic routine going. Pretty well the cheapest looking over the sea, five very basic net-and-fan rooms, attached cold shower etc.
The stars for us are the warm welcome we get from Lucky and Pemma - often tea is provided, and if you're lucky you'll get a bit of fruit as well. NOTE - they don't provide any meals. The other star is the balcony overlooking the bay (you can't see the beach because of the sea wall, built a few years back to keep the sand off the road). It's huge, shady, and shared by all guests, clothes drying area, tables to eat your own food on. Some people stay for literally months, so it's pot luck whether you get a room, but worth asking.
Be warned, it's not for party people - two of the rooms open on to the balcony, so late night drinking is firmly discouraged. But as a base to put your gear and hang out in what is still one of the best places to stay in Sri Lanka, it takes a lot of beating.