Players will go wherever the best loot is pretty much regardless of how much fun that activity is for them. In D3 there were a huge number of people farming up money by breaking vases in the Royal Crypts in Act 1 of Inferno. The Royal Crypts is full of vases that have a lot of cash in them and because the monsters there are utterly trivial and few in number the farmers could safely wear nothing but Gold Find gear while they destroyed the mighty and evil Vase over and over again. Of course they complained that smashing furniture for gold was just causing inflation and wasn't fun (but they did it anyway) and Blizzard lowered the amounts of gold that come from vases in response. Now people complain that Blizzard is evil for nerfing their favourite farming method... ack.
The intent originally was that people would kill packs of elite monsters to build up their Nephalem Valor buff and then go beat a boss to get a big bonus from the buff. This was intended to stop people from simply doing endless single boss runs like was the norm in D2. 20 Mephisto runs / hour, anyone? Unfortunately this seems to have had the effect of locking people in to doing only the areas before the most farmable boss over and over and making those that can't beat the boss or who take a long time doing so feel left out. The new solution coming in the next patch is to lower the minimum number of rares for a boss kill (assuming a full stack of Nephalem Valor) to one and give all packs of elites a minimum of one rare drop. If you happen to really like killing the Butcher you can still go get him but it seems that by far the best strategy is going to be to just roam the world murdering groups of elites as fast as possible without leaving the game. I think this is a good decision. It will be very reasonable from a loot optimization perspective to fight in all kinds of different areas and that will keep the game feeling more fun I think.
The other thing they seem intent on doing is flattening the loot curve. This is especially important for weapons which are pretty much entirely defined by how high the damage bonus on them can be for a simple blue drop and it looks like people in earlier acts will be able to get higher end weapons. Given that the monsters in earlier acts die drastically more quickly and with fewer deaths I expect this will encourage people to farm in easier areas and make it more profitable to do so. It should definitely have the effect of letting those stuck in a1 or a2 eventually grind up their own loot to progress even if the time taken to do so is still quite large. The other factor that is going to make farming in easier areas profitable is that the penalty for death is going way up. Instead of 800g / death we are likely going to be seeing 4000g / death instead. That isn't a tremendous amount of money but dying multiple times to each elite pack is going to become a sizable drain on income and will encourage people to play in areas where they won't die much. This might even mitigate the outrageous farming advantage that ranged classes have at the moment because a tough melee character who can clear an earlier act in complete safety is going to pay nothing in repairs and a glass cannon ranged unit is still going to misclick and die regularly, much to their detriment. I think Blizzard really wants to send the message that the intended way to play the game is not to play in areas where dying constantly is the norm.
Initially I was pretty disappointed with crafting in D3. The jeweler seemed completely useless beyond his ability to take gems out of gear and the blacksmith was a total waste of space. I think though that this is changing rapidly in the endgame. The best recipes are extremely high level rares with 6 properties and crafting them is going to be very much worth the investment. The trouble right now is that there are very few of those recipes floating about and the lower level recipes create items that can be much more easily found on the ground or in the Auction Hall. The crafting costs for everything but the highest level recipes could be drastically slashed and the only effect would be to allow people who play solo to more reasonably make their own gear - I think that would be a positive change. Same goes for the jewelcrafter - every gem combine below Flawless Square should cost 0 gold and 2 of the lower quality gem to allow people to actually crush their way up to something nice.