Something I always forget about until I rewatch old episodes of it is how good and atmospheric the music was for classic Who Wants to Be a Millionaire?. It actually instilled a sense of dread in me as a child watching it when players got to the higher levels. The music builds upon itself...until you hit the million dollar question and it's all stripped away to just this droning tone with heartbeats. The lighting really adds to it, but it was the music that made it so nerve-wracking to me as a child.
Now, since I grew up in the United States, what I didn't know until much later is that they actually had an evil version of the winning cue if someone blew it on the million dollar question. It only played in the US one time, and never on the British version. Other international versions use it much more frequently.
If I had heard this at age 10, when the show was at its peak of popularity, I probably would have found it terrifying. Fortunately I first found out about it last year on TV Tropes and from the comments section I learned what Barney Errors were, so it ended up being funny instead.