Hi, I have been to Kavieng twice and loved it both times. The diving is in my opinion some of the best in the world with everything from pelagics to critters, sharks to mimic octopuss. Both times I have stayed on Lissenung island and found both the island and the dive operation to be great. Dietmar who runs it and his staff know where to find anything and everything in the area and will go out of their way to make sure you see everything you want to see. Some of the dive sites such as Albatross channel, Peters Patch, Helmuts reef are great if there is no current and simply amazing when the current is running. More pelagics than you can count and if you look about so many other things such as Pygmy seahorses, ghost pipefish, etc.
While we were there in February some other divers joined us that had been diving with the other operator in Kavieng as they had not been happy with them, but I don't know anything about them. As far as diving in the caves, I have not been to them as I am not a qualified cave diver and I know that Lissenung does not offer cave diving since they are not cave divers but the other operation does dive them so I assume they are qualified cave divers.
I am sure you will have a great time there, wish I was going back anytime soon!