The small Weligama Bay Dive Center has professional and friendly staff. They are experienced in taking people for their first try dive (discover scuba) and with open water courses as well.
It definitely is a wonderful place to learn to dive.
While the diving is maybe not world class there are many little things to find for more experienced divers. There are only a few coral, but plenty of fish life and smaller critters like nudibranchs. One big plus is that there is only one other dive shop in the area so the dive sites won't be overcrowded.
Visibility can change a lot depending on the weather and ranges between 5 and 20m.