Munchkin from Steve Jackson Games has a very simple premise, now using the game-board / dungeon itself to keep score. Cards are used to determine a lot of gameplay; it is not a CCG, though. It's also very social, as you can make & break deals with your fellow gamers as you go. Opportunities for betrayal abound. 
There are various Munchkin boxed sets, with different themes, or you can also pick up different themed packs of cards to bring to the game. (Those optional booster packs contain all the cards for that series or license; it's not a CCG)
Here's Wil Wheaton & pals giving the basic one a run through:
https://www.youtube.com/watch?v=V6oMBSiL7Zs

There are various Munchkin boxed sets, with different themes, or you can also pick up different themed packs of cards to bring to the game. (Those optional booster packs contain all the cards for that series or license; it's not a CCG)
Here's Wil Wheaton & pals giving the basic one a run through:
https://www.youtube.com/watch?v=V6oMBSiL7Zs