I ran it today for my son. He played an elven cleric sent to investigate the wailing and make sure the witch knight wasn't coming back. He managed to avoid the snake while exploring the island until it finally lunged at him near the shore and he ran away and entered the tomb.
As a cleric, he just blasted the first skeleton, but left the others alone. He figured out the trapped hallway and went around the other way. He dealt with the group of toadygugs by using "cause fear" to make half of them run down the trapped hallway to get blasted by the skeleton with the wand.
He dealt with the stone knights by making called shots to knock the skulls off three of them (and being lucky that I had a lot of bad rolls for them to hit him). He faced the Witch Knight in total silence because he used a silence spell to stop the screaming head. They went back and forth for quite a while hurting each other and healing themselves until the cleric finally won with only 1 or 2 hp left.
He went back to get his boat and said "I'm gonna go back to the temple and rub it in those monks' faces who thought they could get rid of me by sending me here." (He had very low charisma so we said he really annoyed the others at his temple and that's how he was assigned to go check out the dangerous tomb.) "I'm gonna drop these skulls and loot in front of them and say 'Ha! You didn't think I could do it, did you?' Oh, dang! I forgot about the snake!"
We ended it there on a cliffhanger as the snake's coils breached the water's surface near his boat.
Great little adventure with a good variety of combat, exploration, and puzzles.