Check this out: http://www.videohelp.com/dvd
And this: http://www.dvddemystified.com/dvdfaq.html
I think the most pertinent information would be resolution and bitrate. In the page I linked to, it's not explicily stated, but comparisons with other formats use the bitrate figure of ~5000kbps and above for DVD. That's a pretty good minimum figure for a commercial quality DVD, less than that and it's likely you'll be able to detect artifacting of some sort. (If you're alert and know what to look for. Also, your display must be adequate. This of course, excludes those folks who claim no difference from original with a 40% backup in DVDShrink. )
Here's a free, bare-bones bitrate viewer:
What you're most interested in is the average. (The bitrate should of course be VBR for best quality). As to resolution, for example Media Player Classic can show you this if you right-click the screen and then View -> Information. Any commercial, pressed DVD from a major studio should be 720x480/576, but I suppose you never know. There are other, smaller legal resolutions for DVD.
Now, a DVD may qualify per the above and still be encoded badly, it happens.
[EDIT] I should clarify my statement about artifacting. According to DVDDemystified, artifacting may "occasionally" be noticeable anywhere from ~3.5 to ~6 Mbps. Much depends on the source, that is, how much "action" there is. A talking heads movie may be fine right down to 3.5 Mbps. But ~5 Mbps is a pretty good bitrate for full D1.