Hovering over stats should give more detailed explanation for the specific stat.

For example:

For ATK - How much bonus damage does it give before subtracting the enemy DEF.
For DEF - How much damage it prevents.
For Crit - What is the chance to crit + crit damage (in percentage).
For Block - What is the chance to block + block amount (in percentage).

Also, it would be awesome if all stat names were synchronized (power = strength, armor = defense and the like).