Yes, however, to appease the pedants out there, saying Gygax and Arneson and the rest of the Geneva Lake crew "grew up on" DnD is a bit of a misnomer. They didn't grow up on it, they invented it, and they were well into adulthood at the time.

Agreed. It's why I have all of Kobold Press's supplemental monster books. Variety is the spice of life, and I'm constantly trying to find ways to make combat more engaging than just slugging it out with my players. Quirky stat blocks help me come up with scenarios.

Supplement books or make your own monsters. I love making a custom monster. I had really fun encounter with a custom ooze that could use engulf as a legendary action. Fun to have it chase the players around the map

Assuming they started in the crib, yes. If you were about 10 like in stranger things, that’s 60’s/70’s.

I just explain it as "LOL zombie apocalypse werewolf destroys your character if it puts them at zero hit points ... but 2024 5e thinks it's fine because they removed all its resists and regeneration". Or "It's a Carrion Crawler, failing one saving throw means you are permanently afflicted ... yes you get a new save every six seconds, but you automatically fail it forever".

Harold "Wisconsin" Johnson is the answer to your question. Actually got to meet him this past Sunday in Lake Geneva, WI at the "Dreams and Nightmares" Convention put on by the Wisconsin Historical society. Also got to meet Tom Wham, who is the original artist for many creatures in the original Monster Manual including the Beholder. Wisconsin Johnson was hired to to be an editor of the original first edition books. His degree from Northwestern University is listed as a BS in Biology. What that doesn't tell you is he minored in European and Eastern history. He has extensive knowledge of European, Middle Eastern, Sumerian and Asian mythologies. He used that knowledge to add to the AD&D compendium. He drove a lot of design and content in the 1e days at TSR as he was promoted very quickly after he was hired. Also, there is a AD&D Monster Manual II that is even larger than the original. As to why he is called "Wisconsin Johnson". He loves to wear hats, especially at conventions so that people could find him. He settled on wearing a Fedora exactly like Indiana Jones wore. Someone even called him "Indiana Johnson", but Harold stated emphatically that he was from Wisconsin. So the moniker Wisconsin Johnson was born. Yes, he was wearing his Fedora this past Sunday at the convention I attended.

I actually do not miss the powerful save-or-suck mechanics as "roll the dice to see if you get to keep playing" is more randomly punishing than fun IMO. But getting rid of damage type resistance doesn't make any sense, as that's one of the few ways weapon choice actually matters! Giving monsters better initiative seems like a good idea, because otherwise they risk dying without getting to actually do much. Making creatures like Gith and Gnoll, Aberrations and Fiends etc. makes sense, and gives a bit more meat to the creature types. But having them not be humanoids also seems really weird. Either they should be both, or "humanoid" should be renamed. So it really seems like a mixed bag to me. Good well implemented ideas, good poorly implemented ideas, as well as oversimplifications.