In recent Patch 1.0.8 PTR patch notes, you could see that Blizzard has tested the Monster Density a couple of times. According to the community manager, it is the experiment of the Developer to see what kind of Monster Density do players like in Diablo 3. Do you prefer the clumpy Density with Larger Monster Groups or Scattered Density with Increased overall monsters?
Clumpy Density with Larger Monster Groups: The typical example is the Vault of Assassin in Act II. As soon as you finish one pack of Elites, you would come across another walled and fire-chained Champions. You do not have to search the Elites. They would be just right there waiting for you to slay. If you hit and run, you would kiteflying several packs together and end up dying. But it is pretty awesome if you could beat them all in low Monster Power.
Scattered Density with Increased Overall Monsters: This would remind me of the monsters in Act III of the Keep Depths Level 1-3, Tower of the Cursed and the Tower of the Damned. You fight a group in a distance and then the other. There are plenty room for you to kiteflying the monsters. But you have to run several maps to kill the same amount of Elites like in Vault of Assassin. For those with low movement speed, this would waste a lot of time on the way. But this is better than the clumpy Density for Wizard and Demon Hunter who would like to keep the distance from the monsters.
Just the Way in Patch 1.0.7: I guess a lot of players would stick to the current density. They have get accustomed to the situation. Any change would mean disaster for them. After all, there is no new elements added. It is just the density change. They would rather get some new things rather than this.
Which category do you belong to? Make your choice and cast your vote.