Throughout the process of playing through card games I have found that I really like the shop mechanic in DC the Deck Building Game. It gives you the choice of what card you want specifically, but only to a limited degree.
I also really like certain card or the player having unique abilities, it makes the cards not just feel like a re-skin. Plus the creator(s) can get really imaginative with this by coming up with new abilities, for example: Buckled down – gain +3 str and -1 speed.
Event cards in my opinion is what really makes a game fun if done correctly. I love the idea that anytime when picking up a card, that it could change the whole game in an instant.