I could continue rambling on about reason why I don't like Apple's 3D dock, but I think I'll save my time and just show you how simple it is!
1.) Simply open Terminal (Applications/Utilities/Terminal.app) and enter the following code.
defaults write com.apple.dock no-glass -boolean YES
2.) Now all you have to do is kill the dock and you should now see the 2D dock.
Other Notes: It is incredibly easy to reverse this if you want the 3D dock back. Use the same command shown in step 1, instead using NO at the end.
defaults write com.apple.dock no-glass -boolean NO
Feel free to post your opinions on the 3D dock in the comments section.