Good luck in The Dark Ages!
The central themes in Dominion: The Dark Ages are the ‘Destroyed Cards’ pile and upgrading. There are cards that do something when they are destroyed, cards that directly affect the ‘Destroyed Cards’ pile, cards that upgrade themselves, and cards with ways to upgrade other cards.
Dominion: The Dark Ages can only be played in combination with Dominion or Dominion Intrigue. This is because you need the Victory and Money cards from those games.
This expansion contains 500 cards and adds 35 new Kingdom cards to the game, plus various negative cards that you can give to other players (Ruins), new cards to replace starting estates (Shelter), and cards that can only be obtained via certain other cards.