While d&d 3E was full of blessings in comparison to old AD&D, I think the best thing about it was the actual institution and enforcement of standards.
3E's rules were by no means perfect, but they were structured enough that you could go to any gaming table and know you had a pretty good chance that you didn't have to re-learn the game's rules all over again (hell, you could even play your character from your previous game mostly as-is). The rules stayed mostly the same from table to table.
And that's why every viking hat on twitter spewing rules-are-bad rhetoric (i.e "it's all guidelines!") to me sounds like this:
Rules exist so we can all agree on what game we're playing. They set expectations and ensure players can make informed choices (starting with the most basic choice of whether I want to join your game or not). Like most adults, I'm a busy person, so If I'm going to give you three hours of my time (or possibly 7, if commuting in meatspace), I better be damn well sure of what I'm getting. I don't sign blank cheques with my time.
I'm thankful to all those GMs that honestly answer the questions I ask them about their games and houserules, even those whose answers tell me I wouldn't be a good fit for their game (or rather, I thank especially them, since their honesty keeps me from wasting both my time and theirs).
It was supposed to come off as a longer rant.