My issue, is that it is too easy to make the game "easy". For those that want an easy and stress free time of the game, the game is already fairly simple, and there are three difficulty settings to fall back to that offer up what they need. However, at the other end of the spectrum there is not an equivalent. Sure master pumps things up, but it is simply a multiplier that does not change the real difficulty of the game, because what is already there is not hard.
The problem goes back to the core of the mechanics in the game. If that were fixed, everything would fit together in a more coherent way. I am firmly of the belief that better balance, makes a game better, and I am not talking about cutting things or knee-jerk fixes and nerfs, I mean actual thought out balance.
Properly balanced gameplay mechanics would give people more of a reason to make more characters. The more competetive builds there are, the more you'll enjoy trying out completely different and unique builds.
For example, if crafting wasn't so blatantly overpowered, you would have a real choice between the different perks. Do I make a mage that focuses on getting better gear at the cost of some other useful perks, or do I skip crafting? Right now, if you want the most powerful character, you always know to pick crafting. If you're choosing something else, you know your character will be less powerful because of it.
It really bothers me, that many people seem to be so apathetic or hostile to the idea of good game balance, because they think it would destroy their freedom, where if it is done right, it would make it even better by providing even more choices.