Taken from my steam review:

Innovative deck building game that utilizes some unique mechanics and effects.
For example:
since your deck size is effectively your HP, there is a shop that lets you purchase cards through permanently exiling other cards from your deck
cards that add negative cards to your deck when you play them aren't necessarily bad, since these "curses" absorb damage and there are even effects that benefit from them
Do you use the damage of Death to kill the enemies in the current encounter, or do you get them on your side and team up against the Grim Reaper himself?
The art style, interesting events that spice up the gameplay and an active development team that keeps adding more features and listens to suggestions from the community combined with a very cheap prizes makes Blood Card a game that every fan of the genre should pick up.

As for the biggest downside: at some point in your run, you really need to get your deck to do some broken stuff or you will probably just fail. While the game already has >200 cards and 2 alternative characters that use a different ruleset, some of the keyword abilities only have a couple of cards assoziated with them and the Bloodwitch character needs some love from th developers before it can be considered a real alternative to the default char.
The initial wording of some cards was a bit confusing, but I am in contact with the programmers to improve the wording.

Like I have already written in my review, the game mechanics allow to implement some cards, events and effects that you simply don't see in the most deck building games that I am familiar with. Considering that this is a roguelike game with permadeath and random events + various different enemy groups on your path to victory, the resulting decks tend to turn out quite strong - almost like you were actually building a constructed deck.