I played in it during the 1e days. We solved U1 without much hardship, seeing thru the fake hauntings and then taking out the bad guys without much difficulty. We moved on to U2 and solved it diplomatically in like 10 minutes. The DM was a bit pissed that we'd figured that out, I think. We moved directly to U3, but of course our diplomatic solution had left us fairly inexperienced and the tougher combats in U3 shredded us. After suffering heavy losses, what was left of our group left.
I obtained the adventures from my previous DM, and ran them for a different group in the late 90's using 2nd edition rules. They handled U1 w/o much problem, and they too managed to reach a diplomatic solution to U2 after just 1 minor skirmish outdoors. I ran a small adventure in between U2 and U3 to boost them up and then provided them with dozens of lizardmen and human guards as extras for assaulting U3. We used tokens on a smaller sized grid and managed to achieve the objectives in U3 w/o suffering any party losses. But most of the lizardmen and other guards bit the dust. They managed to conquer a few of the bigger foes like the priests and one of the giant sharks. The shark actually swallowed one of the characters, but the party cut them free before they died.
I wound up using U1-U3 as a prelude to the Evil Tide/Night of the Shark/Sea of Blood series. The underwater gear found in U3 was of great aid here. IIRC, the party completed the first one, but the campaign ended due to other reasons before they finished all 3.