I still miss some of the features that Discworld Mud had, and mainstream gaming hasn't warmed to. Strange currencies, complex banking, different in-game languages, convenience features gated in RP ways (the Taxi guild of portal wizards!), etc. The conventional wisdom holds that that'd be far too much friction for modern games, but it contributed so much to making the world feel more than an inch deep, which is something modern gaming needs all the help with it can get.
I also think scripting in LambdaMOO may have been my gateway drug to coding. Once I learnt I was able to expand the world myself, I was intoxicated. Yib's Guide to MOOing [0] is a great read for anyone interested in how that all used to work.
And the social scene of these services in the 90s and early 00s is hard to describe. Honestly, @go #17 in LambdaMOO at its height felt more like the Metaverse to me than anything Facebook has made to date.