It seems to me that when games cater too much to casual gamers, the games get "dumbed-down". The strongest example would be the Elder Scrolls series. Morrowind was a fantastic game for hard-core gamers and casual gamers alike... without compromising gameplay. However, with Oblivion, they catered to casual RPG gamers a lot more, and the result was an over-simplified game world.
You can't please everyone. I too am a big DD fan, but I find Morrowind to be inferior to Oblivion. I will list a few reasons--not to start a Morrowind vs. Oblivion discussion, but to highlight some of the features that make a good game.
Graphics: The graphics in Oblivion are superior.
Stability: In spite of my computer being able to run Oblivion with no trouble, Morrowind crashed it numerous times and even caused my machine to reboot.
Inventory Window: The one in Morrowind was very cumbersome.
Alchemy: Alchemy is so cumbersome to use in Morrowind that I totally abandoned its use.
Combat: Switching between the use of magic and melee was a pain in MW; it was well done in Oblivion.
Map: I spent boring hours in MW searching for stuff. This did not enhance my experience--it detracted from it.
Both games could have benefited from a more rich outdoor experience. At least Oblivion's was easier to get around in.