I couldn't say what would have happened over the last 10 years, since I did quit right after Trammel came out. You see, back then I was a big fan of the game as it was. After Trammel came out, 90% of my friends moved to Trammel and I never saw them again after I decided that Trammel was boring (remember, that was then). Felucca was no longer interesting to me because the people I used to defend had all moved to where they didn't need defenders any more.This is so funny, seeing everyone say the worst thing for UO was Pub 16 and AOS. Those are probably the only reason most of us still play. I played before 16, just before trammel came out....like 1 month. If Pub 16 and AOS never happened, would you honestly still want to play the same damn thing for 10 plus years? I think not. Every single person in the game would have a Silver Indesructable Supremely Accurate Katana of Vanquishing, killing liche Lords in Deceit. There would be no diversity between skills, and disputes over taming and this template is so much stronger than that template. These changes are what makes UO the best damn MMO out there. I for one am with the Development team and the changes and additions they make to the game.
BEST CHANGE: EVERYTHING, keeping UO the best damn MMO out there!
WORST CHANGE: Cant think of one!
I had a friend, early on in UO (who also quit with Trammel), who always said, "Everyone wants to be a king, and nobody wants to be the citizen." His comments were about the roleplaying community, but it fit UO as a whole perfectly. It fit any MMORPG for that matter.
So while for the 90% of my friends, the creation of Trammel was a good thing, for me and the other 10% of my friends, it was game breaking. And if I survived up to Pub 16 and AoS, they would have been just as game breaking to my play style back then.
I admit to being in the minority, even though many posters here seem to agree with me, and from a business perspective all of those changes were good changes (yes, even AoS). But for me, they were the worst things they could have done to UO.