Here's an interesting video on the many issues remastering Buffy the Vampire Slayer to high-definition has caused, simply because they haven't consulted the original filmmakers. I'm currently watching the show via Amazon Prime and their stream is mostly in widescreen (I believe it's essentially the widescreen UK DVD release), and that occasionally throws up some "blunders"--mainly film crew being visible on the edge of the 16:9 ratio screen, although recently I could see the "off camera" wires being used to make it appear like a keyboard was being used by an invisible Buffy...
However, the HD remaster appears to involve more egregious changes than moving from 4:3 to 16:9 ratio--such as colour tinting that goes against what the episode's director intended (most unacceptable when nighttime scenes appear to be taking place in daylight), and framing changes that mean there's too much space above actor's heads. Anyway, take a look for yourself. It's a very enlightening and well-constructed video that compares the original episodes with the remastered ones. I actually think some of the changes are improvements (appearing clearer and richer), but I didn't make the show and would rather see the filmmakers consulted on all these alterations. That's what happened with recent HD re-releases of Star Trek: The Next Generation, Twin Peaks (with David Lynch) and The Wire (with David Simon), so why not Buffy?