I think a lot of producers/engineers are having difficulty deciding on how to set up DD5.1. Some people put way too much in the center channel, leaving almost nothing for the other 4/5/6 speakers to do. Others put way too much in the rears, so it sounds unnatural.
About the only DVDs I purchase are music DVDs (I rent movies). The music DVDs, if DD5.1, can sometimes be really irritating.
I recently bought Roy Orbison - Greatest Hits. The sound varied a lot from "mono" (center) to 5.1 with a lot from the rears. They discussed this in the liner notes saying they were trying to maintain the original "ambience" in the "mono-sounding" tracks while taking advantage of DD5.1 in others.
Some songs were really weird being close to "mono" for most of the song, until the crescendo, near the end of the song, when all hell broke loose. I'm glad they included this information in the liner notes, because I would have thought it was just poor mixing all the way through....
They did a comparison of mono/DD5.1 on one of the tracks and this actually didn't sound bad.
Roy's DVD is also DTS. The DTS track was about 5dB louder than the DD5.1 track - not good for comparisons between the two. I almost like the DD2.0 track best for most of the songs.