Right now some cards are still probably at least a bit overpowered. Every Unit card typically does something positive on top of it's stats.

General design principle: a base Unit costing 0 is a 1/1, a unit costing 1 is a 2/2 etcetera. Typically every card has at least some gametext and ability on top but abilities like Flying are considered more powerful. Keep in mind that every card costs 1 Mana to draw. And sorceries are more playable than Units since they don't require an empty slot.

Typically direct damage to opponent is something I wanted to limit since it requires less strategy on the board. But it's nice to be able to finish off games with them if you are close to winning anyway.