I'm obviously old because my retro games are a lot older than your retro games. I started playing Colossal Cave Adventure on a TRS-80 in the mid '80s. However my very favorite game of all time... the one I have more hours in than any other... is Nethack. I still play often and nothing is ever going to touch it for me.
Yes it uses ASCII graphics with a top down model where the NPCs are all letters and numbers (you are the mighty @ symbol) and you'd really have to want to play as you need to set up Putty to connect to the server but still... never have I experienced such fantastic game play from a title that is VERY hard but winnable.
https://www.thegreatestgameyouwilleverplay.com/
Here is the wiki but I highly suggest you give it a go without any additional information. You WILL seek it out once you die the 25th time.
https://nethackwiki.com/wiki/Main_Page
North American Nethack server:
https://alt.org/nethack/
Just as an example of some cool mechanics. If you kill a cockatrice and you pick it up without gloves, or you eat it, or you trip over it on the floor (blinded) you turn to stone and you are dead. It takes a few turns though so you "can" stop it with the right action.
However, if you kill a cockatrice and you ARE wearing gloves you can pick it up, equip it as a weapon and one shot most NPCs by turning them to stone.
When you are logged in and playing others can watch your game and send you "mail" to give you a hint and what not.
Game is very hard. Takes some work to set up an a bit of practice to get the movement down. Still I've never had more fun playing a game. I highly doubt anyone would want to try it but if you do hit me up and I'll help.
Diablo? Based on Nethack but nowhere near as good.