Both dealer cards are exposed
Dealer wins on all ties, except on a natural blackjack
Player blackjack pays even money
Player may split only once

Rules that can vary include but are not limited to:

Dealer hits or stands on soft 17
Tied blackjacks either push or go to the player
Player may or may not double after a split
Player may double on any first to cards or not
Player may split more than once
Player may or may not split unlike 10 value cards (for example queen and king)
Following are some actual places that offer double exposure, the specific rules, and house edge. Sometimes the game goes by other names like "Dealer Disclosure" or "Face Up 21."

Tropicana, Claridge, Taj Majal (Atlantic City): 8 decks, dealer stands on soft 17, double only on hard 9-11 and soft 19-20, double after a split allowed, tied blackjack wins, split only once. House edge of 0.66%.

Stratosphere (Las Vegas): 6 decks, dealer hits soft 17, double on hard 9-11 only, double after split allowed, tied blackjack wins, split up to four times. House edge of 0.68%.

Lady Luck (Las Vegas): 6 decks, dealer hits soft 17, double on any first two cards, double after split not allowed, tied blackjack wins, split only once, jack and ace of hearts pays 2:1, suited 6-7-8 pays double. House edge of 0.26%.

Circus Circus (Reno): 6 decks, dealer hits soft 17, double hard 9-11 only, double after split not allowed, tied blackjack pushes, split only once. House edge of 1.47%.

Grand (Tunica): 6 decks, dealer stands on soft 17, double on hard 9-11 only, double after split not allowed, tied blackjack wins, split only once. House edge of 0.96%.

A note about the suited 6-7-8 bonus at the Lady Luck. The only exception to the basic strategy when the dealer hits a soft 17 is to hit a suited 6 and 7 against a dealer soft 12. Also note that the double exposure tables at the Taj Majal and Circus Circus are only open on weekends.