Yeah, the picture quality is pretty bad. Same goes for the early seasons of DS9. Funny though, when you watch Part II of Descent you'll notice a huge improvement in picture quality compared to Part I. For some reason, season 7 looks a hell of a lot better on DVD.
The picture quality is better for season 7, but I'm noticing trails when there is movement onscreen. I never noticed this problem with the season 5 & 6 discs, or any other DVDs I have. I think my DVD player just doesn't like TNG.