In my second playthrough I discovered a lot of stuff I overlooked the first time, like the area under the Miller's house and the location of the Doctor who cures Eugene/Clyde, the quest involving Sir Robin, Bellegar's "moral choices" cave, and a lot more. I also accidentally killed the chicken that NPC in Broken Valley got soul-forged with, which was kind of funny.I checked a few walkthroughs just to make sure I'd picked up all the quests, but there are a few things the walkthroughs don't include as quests, like the 3 sleepers. I also found that there are areas you can swim to around Sentinel Island and gather a lot of loot if you can deal with the wyverns.
One thing I only discovered about the three sleepers in this play-through is that they do actually turn up in Broken Valley village after all: I'd expected them to be in the Black Boar like every other wanderer, but they hang around at the back of the village between the chapel and the talking vendor's cart thing, and reveal that their ordeal started when a bottle of wine was provided by a "weird rhyming fellow"!
