I'm a new player, so this may be an issue that irks me to a greater degree than it does folks that have more experience in the game.
I really dislike the fact that it's hard to get hard-and-fast numbers for damage or defense for items in this game; it makes it very difficult to plan out what affect equipment will have. Items have different bars whose length determines how strong they are, but it's hard to translate that into real-world damage.
So... it's doing normal damage? Great! What is the difference in terms of damage value between 3 bars and 4? What affect will leveling up the item have? How much damage will it do to which type of monster?
This issue is even more mystifying for newer players when it comes to defense. There are a ton of defensive options, but WHAT they actually defend against and which monsters use which type of damage is a mystery. I have no clue what armors to look forward to, other than via vague word of mouth on the forums (which is often outdated, given the lightning-quick buff/nerf cycle of the past few weeks).
In general, I would like for there to be more transparency with respect to items and their affect on play performance in the game.
To be honest, we had numerical statistics for defence, but that whole thing was replaced with the current stat calculation system.