From what I've seen of it, I honestly don't think TTD'90 was too bad. There really isn't that much of a change in format, and I like how the bonus round offered a second chance if you didn't uncover 3 in a row. Still somewhat luck-based, I guess.
And, this may border on blasphemy, but I didn't think Patrick Wayne was a bad host. Nothing outstanding, but I'd take him over, say, Donny Osmond.
But I think Seth's list is the most convincing argument for why TTD'90 (and every other show that came out that year) failed. It was nearly suicide for the genre.