So after playing OD&D followed by 1st ed computer games (Pool of Radiance...the original...up through Dark Queen of Krynn), followed by Mage: the Ascension and a little Call of Cthulhu, I played no RPGs with real people for about 25 years.
Then I had the chance to join a 5th Edition game. While I had followed along with many of the changes in D&D by reading the books over the years, I was quite surprised nonetheless at many things.
A spectre showed up, and I pooped my pants. I immediately started running away. Imagine my surprise when it hit another party member, and...their max hitpoints went down, temporarily.
I thought, wow. "You used to lose two levels of experience, permanently!"
I also found a lot of the spells I remembered had been nerfed. "Wait, Fire Shield does 2d6 damage to the person attacking you? It used to do double the attacker's damage! Hold Person requires concentration to maintain, and only affects one target? Haste only gives you one extra attack?"
I'm curious to hear what other funny stories of edition 'jumps' people have to relate.