I've also been watching the old games on Netflix. Specifically, so far I've seen Season 1, Episode 1, and Season 2, Episode 1. Fascinating to see the way the show was presented early on.
The most obvious difference, apart from Alex's appearance, is that he did a lot more explaining of how the game worked in the early days. Today they just take it for granted that everybody understands the game, but back then he started off by going through how the game was played in case anybody wasn't familiar. Also, the "end of round" sound effect was a lot more obnoxious! And in the first season, you could ring in as soon as you knew the answer! They didn't go to the "wait until Alex finishes reading the clue" rule until the start of Season 2. Alex specifically announced the change in the rules, and said it was to make it easier for viewers at home to play along.
A couple of curiosities: You'd think that Season 1, Episode 1 would be the first episode ever aired. And yet it had a returning champion who had somehow already won 2 games. Wha??
Season 2, Episode 1 featured a misspoken contestant response. Someone said "What is The Hounds of the Baskervilles" (rather than the correct "Hound"), and Alex accepted it. These days that would get corrected later, and the contestant would have had some money deducted. But they let it pass, and never corrected it. Shocking!
And even then, there was the occasional contestant who started in the middle of a category!
It's fun to see the way the game was played in the early days.