MF'ing isn't fun. I understand the reasoning behind why they switched the focus from bosses to elites, but that doesn't make it more fun. They wanted to reduce the effectiveness and even the demand for 3rd party botting programs, but what it left us with is a very anti-climatic gameplay. I think I can speak for everyone who played Diablo 2 when I say that boss runs were very fun.
Items aren't fun to find. There is too much randomness on the items to be excited to see anything drop. Anyone remember while playing Diablo 2, the rush you got when a unique ring dropped, just before ID'ing it? Even if it was just a nagelring, it was still awesome! I haven't felt that way even once in the 120 hours I've put into Diablo 3 - I can get that feeling even now in Diablo 2 in less than 20.
Difficulty doesn't come from requiring the player to be a better player. When there's a very good chance that an elite pack can ruin your day, without any input from your skills as a player, it doesn't make for a fun time. What is fun is exposing weaknesses, taking advantage when an opponent leaves an opening, and even being punished for making mistakes. Many of the bosses are actually fun and apply these ideas, but as previously stated, bosses are nearly pointless to farm and the good loot is found on stat-bag elite packs whose potential to be killed is way too situational and take way too long whether or not their mods allow your build to handle them.
All of these issues have one very clear motive, and I hate to sound like a conspiracy theorist but it's starting to make a lot of sense. It is apparent to me that Blizzard doesn't want us getting past Act 2 of inferno without spending some cash at the RMAH. If you elect to not use the RMAH, you'll be grinding and selling items 10-100k at a time, saving up for that 10 million gold weapon that will still require you to kite in order to farm. I'm not saying it will be impossible to avoid the RMAH, but it will be practically unfeasible. People have complained about the lack of offline mode, and I believe the motive is two-fold. DRM always increases sales, that's why it is utilized even if customers hate it. The other part is that they want you to have access, and the incentive, to use the RMAH. The brick wall that starts in Act 3 of inferno, the randomness of the gear and the admitted controlled-rarity of good gear, all of it points towards the RMAH and I believe that focus takes away from what the experience of a Diablo game should be.