Visit scenic Kingsport, the fourth expansion for Arkham Horror! Although of course this is only the second box to add a new area of the board, and unfortunately Kingsport isn't as interesting as Dunwich. Although it adds several new game mechanics and plenty of new cards, the struggle against the Kingsport Rifts just isn't as compelling as the fight against the Dunwich Horror, and is sort of like the Arkham Horror equivalent of 'doing your chores'.
For Arkham Horror veterans, here's now it basically works: the Rift Tracks on the Kingsport accumulate tokens; when the tracks fill up, a Rift starts drifting around the board, spitting out monsters. The investigators then have to leg it around Kingsport having encounters at various places in order to seal the rift. When a rift is sealed, it goes back to where it started and starts accumulating tokens again. There's no very strong sense of accomplishment, unlike beating that disgusting Dunwhich thingy. Gates don't open in Kingsport - a big mistake in my view - so it's a bit of a dull area of the board and feels quite 'cut off' from Arkham. Getting to the special locations on the cliffs is frustrating rather than challenging, and there's not much reason to hang around in Kingsport having encounters because the encounters are pretty much the same sort of random mad stuff that goes on in Arkham itself.
Of course this is still a pretty good expansion because it adds stacks of additional content for the original game (items, characters, spells etc), and that's all well worth shuffling in. The Guardian/Herald cards are a great idea because they allow the players to fine-tune the difficulty of just about any game. The four new Great Old Ones - Eihort, Y'Golonac, Atlach-Nacha and Ybb-Tstll (or something like that) - are all solid enough additions to the pantheon and are a real challenge to defeat. Like the original AH GOOs they make you take skill tests to avoid being hurt by them, which was an element which was notably absent from the Dunwich lot. Plus, the art on the Kingsport GOO cards makes me feel physically ill, so they've pretty much captured the essence of the Mythos there, at least.
My suggestion is: use every card in the box, but ignore the Kingsport board itself and all that rift nonsense. Or come up with some house rule that allows gates to open in Kingsport, just to keep everyone on their toes.