Well, I have definitely learned that audio is much more subjective than video.
While I was at RadioShack, I picked up some full size headphones in their brand, which were $30. I did because it had the adapter in them and I thought I could kill two birds with one stone by testing the headphones to see if they worked if the included 1/4 adapter didn't.
You guys will laugh but at first I didn't notice much difference between the RS and the Denon's. I then switched back and forth and started to notice much more of a difference. This just proved to me that what you have at the time is better than anything else out there. I noticed there was less extra noise and that the mids were much more clear as well as the voices. The bass is also much more smooth deep comparably. All I am saying is the two sounded similar while the Denon's are certainly far superior.
As far as the 2000's vs the M50's... meh... not a huge difference with music listening. Everything does sound more smooth and refined though. What I really switched for was the comfort. These things are DAMN comfortable. This justifies the price alone. The headband clamps very light in comparison to the M50, almost unnoticeable. The cups cover the ears perfectly, and they are very lightweight.
Overall I am very satisfied. I can't notice a huge difference in gaming because I only play one game and it isn't the best game for testing (BF3 - lots of noises and distractions).