The fact that so many of us still love the programme is a definite testament to how good it was. They say the real test of how good a children's book is is by how many people still like it when they're grown up. I don't see why TV programmes should be any different.
Of course, there's probably not many of us who think all the Knightmare series were good - as an adult I definitely prefer the early seasons - but I'd still watch any of 'em. The Dungeon rules!