1. The exhibits have been pretty heavily reworked. All the Masks that granted the ability of another investigator have been changed to something else. 3 of them let you exhaust to use the other stat in the pair at a -1 in lieu of the original (for instance Will -1 instead of a Fight check). One lets you exhaust and spend a clue token before drawing from the Mythos and allows you to put it on the bottom of the deck. My personal favorite Mask, lets you exhaust to gain any common or unique item you have the opportunity to purchase. The 3 Parchments of the Elder Sign changed to 3 different items (1st/2nd/3rd Elder Sign Fragment) and are more reliable, lose 1 Stam or Sanity to close/seal/remove doom token depending on which fragment you have. The Pentagram of Blood isn't worthless anymore. Now lets you spend X Stam and discard to send a monster with X toughness back to the cup.
2. I flipped through 5 of the encounters for the neighborhoods. They are mostly unchanged, some text clarified (if you don't have X, then nothing happens for example) and the take a Barred from Neighborhood replaced with place a Patrol token. A few of the encounters have changed slightly, for ex the one Velma's diner encounter that requires a Retainer, Silver Twilight Membership or Deputy doesn't require you to discard it anymore.
3. The herald remains unchaged.