I was lucky to play UO from the beta days, when a lot of unintentional "features" existed. To name a few good ones:

* monster gating. Opening a gate (portal) would allow people to travel from one place in the world to another by crossing that portal. The thing is, that also worked for NPE/monsters. So we would go to the craziest dongeons, run around to get the attention of hordes of monsters, open a gate in a tight spot and have this whole group of monster reach some place where they should never be seen. Imagine dragons, Liches & whatnot at the edge of a beginner's town for instance or worse, inside somebody's house :).

* stealing stuff from somebody in the middle of combat/duel, magic required reagents to perform spells, steal regents = win, finish the player with your bare fists.

The combat system in the early days also benefited from bugs that made it nothing short of a dance, it required to be very good at timing and sparked some complex strategies to win (spell interuption, spell pre-casting, weapon hit timing in between spells, etc etc). You could also "pretend" you were casting a specific spell while in fact another one was being invoked. Luck played very little in duels.

It's also the first mmo where team play started to be a big thing, small tight knit group of players using software like Roger Wilco (ancestor to mumble/teamspeak) handling combats against crazy odds.

It was also full of nasty stuff, accounts/houses/gold had a real world value, hacking was very easy back then and rampant.

I could go on and on about stories about Ultima, it was an incredible game at a time where massive multiplayer gaming was being defined. It had me learn how to program, learn the english language, build websites and much more.

p.s. I used to play on Chesapeake, with various guilds (WWW, AdJ, Oinland etc) if anyone from these days is around :)