Man, I don't understand why people hate on Balck Market. It's a luck based card, that is true, but Dominion is a game that combines luck with skill. It's lucky to hit $8 in a BM game or to draw 3 Estates with your Chapel, but people don't hate Chapel for that, do they?
Before I even knew of Black Market (or of promo cards at all) my mother and I played Dominion. We had nine kingdom piles and one pile with 10 random cards in it that we did not see at the beginning of the game. It made the game a ton of fun. Yes, it's very unlucky if your opponent gets a curser or trasher out of the Black Market deck, but you can go for Black Market as well!
Black Market is also fun because it lets you play your Treasure cards during your action phase. This makes a lot of cards awesome, including Tactican, Quarry, Royal Seal, and possibly Diadem. You can also avoid it IRL by not buying it. If you hate Cultist but you love Dark Ages, you are out of luck. If you hate Black Market, don't purchase it to play with. In Dominion Online, there are many ways to not care about Black Market:
1. Don't buy it and build an engine with the 9 other cards.
2. Realize that you play very very few games with Black Market.
3. Veto Black Market (or don't play with it).
4. Go for Black Market because you have the action space or are doing a Poor House thing. You might get something good, but you will always get two coins.
That's just my inexperienced two cents on Black Market, I'm sure if someone disagrees with me they will say why.