There are many tables, charts and simulations for standard Blackjack variations and the % change in house edge that each rule introduces, like this one, for example.
I have come across a Blackjack variant which on the face of it seems very generous, but I'm struggling to work out how much it affects the house edge mathematically.
The variation is that instead of the dealer waiting to reveal his second hole card until after the players have taken their turns, it is exposed from the start.
So you can see the dealer's first two cards before you make any decision as to whether you should stand/hit on your own hand, with the exception of taking 'insurance' against a dealer blackjack.
Is this variation as generous as it sounds?
It is extremely valuable. Any time you have a strategy that says to stand on 17, if the dealer shows 17 you know you have to hit and will win $\frac {16}{52}$ of the time (ignoring used cards). You can also stop earlier when the dealer shows 16, for example, hoping he busts. Unfortunately, this is coupled with the player losing ties instead of pushing them, which is a big downer. If I had to guess, the pair of these changes is more favorable to the house than standard, or they wouldn't offer it.