I'll probably end up using Dunwich as a campaign setting too - IMO that's this book's strength.
I really liked the Return to Dunwich adventure (mi-go under Dunwich? Oh yeah, baby!), even though I thought the d20 stats for the son of Yog-Sothoth were a little over powered.
Overall though, since I missed the original BRP printing I'm very happy with it.
As for The Dunwich Horror - Armitage had to win in the end. The son of Yog-Sothoth was loose, and if not stopped would have helped bring the "end" very quickly.