Super-guild has already cleared Naxx

[Concillian]

I wouldn't consider the mind-numbing simplicity of 99% of Diablo (II), and the associated handicaps to make it somewhat to very challenging a good thing. Variants were things of necessity, rather then something I'd applaud as a good example of game design.

It depends on what you're trying to accomplish with your game design.

Are you trying to market your game to 5% of the total population of gamers? Or are you trying to market your game to 90% of gamers who have the ability to seek difficulty as they see fit.

See the Super Mario games. You can complete them pretty easy, but have some challenge. Once you learn the controls and the tricks, it's not too hard. The hardcore will go back and find all the secrets, etc... Lego Star Wars series, similar theme. Many very good games use this method of appealing to the masses, but providing ways for the user to provide their own challenges.

If you cater to the top 2%, you have a game destined for failure due to lack of critical mass (Vanguard)