There I describe the beauty of being able to freely control a games difficulty!
Blizzard did something amazing and is bringing that function back for those of you that remember if from Diablo II. Below are the simple and easy steps to enable the game changing setting.
This is taken directly from Diablo3.com, and you can find the article here.
Similar to the “Players X” command in Diablo II, Monster Power is a system designed to give players more control over how challenging enemies are in each difficulty.
Step 1: Open up the in-game Options menu (default: Esc) and select the Gameplay tab.
Step 2: Check the box next to “Monster Power” to enable it.
Step 3: Open up the Quest Selection window.
Step 4: Select your designed Monster Power level from the drop-down box near the bottom of the window, under “Difficulty Setting.”
Step 5: Once you’ve set your Monster Power level, quest, and difficulty, click “Select Quest” to confirm.
Step 6: Enter game and profit!
“No Monster Power” is the default setting. Each Monster Power level will increase the health and damage of monsters, and in return players will receive scaling bonuses to experience (for heroes levels 1-60) as well as boosts to Magic Find and Gold Find (for heroes in Inferno) which will stack above the 300% cap. The option to increase Monster Power will be available to all players starting at level 1 and can be adjusted separately for Normal, Nightmare, Hell, and Inferno difficulty.
(Note: If you join a multiplayer game, you will adopt the Monster Level of the party leader. When you leave the party, your Monster Power level will automatically revert back to your previous setting.)
Now don’t get all excited and start trying to do this in your game window, and then call me a liar, because this feature is currently only available in their test realm. But, don’t you worry your pretty little self, this is going to be included in the patch version of 1.0.5