Let's dig into what's changed!
In terms of balance, the following cards have been modified:
Tame - Equip a monster as a sword or shield. (Monsters can no longer be sold for gold.)
Leech - Gain life equal to the value of the selected dungeon card.
Trade - Sell any non monster card for the double of it's value.
Feast - Raise a dungeon cards value by the values of its adjacent cards.
Bash - Use an equipped shield as a weapon. Each attack the shield loses 1 durability.
Suicide changed to Worship (including new card art).
Worship - Redraw 4 random monster cards and gain their values in gold.
Since these are pretty significant, the leaderboards have been reset.
But the main attraction of this update is the new mode called Delve. First of all, it replaces Streak-Mode. In it, you need to gather a required amount of gold in order to win.
But this time, you're descending down a dungeon which gets increasingly difficulty the further you go. If you fail, you'll be pushed back up.
Don't forget that Card Crawl's successor, Card Thief, is coming.