Sorry this is coming to you late I have been a sleep for about two days fighting off pain and a fever.
Card quality is a source of much debate because it runs so close to card quality and tempo. I will even go as far to say that they are often the same. Over the years card quality has been a lot of different things. But, I believe card quality is the weight of the cards ability against its mana cost in the given environment.
Let’s look at some hypothetical examples.
If a cards costs 3 mana lets you draw two cards and another card costs three mana and it allows you to draw three cards. It is pretty clear which of the two has better card quality even though both are good.
For this example the two creatures we are talking about have no abilities. On of them has a power/toughness of 6/4. The other creature is a 4/4. Both share the same mana cost. It is clear that the 6/4 has higher card quality.
In both of the above examples I created hypothetical environments to display how a cards ability weighs against the mana cost of the card. Card quality doesn’t stop there. It is different format to format. Which is why it is a little more difficult to nail down than tempo and card advantage.
One thing that sets card quality apart is that its use really begins in deck construction. When building a deck you often make decisions. The first is what you want to play. For many of us this is as simple as picking a decklist and printing it out. Then you take a look at what you own and check it with the list and measure it against the environment you play in. For example the list might run Demystify, but you might find Celestial Purge a much better choice for your local game store.
Card quality isn’t the easiest concept for players to understand in Magic the Gathering. While it is one that all players should strive to get a grasp of. I think the best key to understanding card quality is to weigh the card for the environment it is to be played in.