Well, DH is not intended to put you in the game environment. Instead it puts you in a simulated room with a simulated speaker system. It does this by stereo channel crossfeed, reverb and HRTF. That can be an disadvantage I guess but at the same time it has advantages too.
The disadvantage: Does not put your head in the environment of the game
The advantage: Works with anything (not just games) that outputs multichannel sound.
I have heard both good and bad implementations of DH. For example on my laptop with crappy soundcard there is a checkbox for DH on/off. This is the bad implementation. The good one is on my desktop with Esscence STX soundcard and HD650 headphones. The soundcard has DH built into it's drivers and it allows for custom DH settings, not just on/off. This means I can tell the DH software how many channels it should use, what kind of room I want to sit in etc. When used right, this setup can be very convincing without actually doing much unnecessary damage to the sound.