In no particular order:

• The CEO Spez decided to edit comments that were directed at insulting him to insult that subreddit's moderators instead (it was a Trump subreddit, but even so), with no indication that the comments had been edited.

• Reddit's redesign, barely anyone who used the old design likes the new one. At least they kept the old one.

• Removal of exact Upvote/Downvote numbers like we have here only giving an overall "score". Later followed by obfuscation of the true value, supposedly due to bot vote manipulation.

• The "jailbait" subreddit, which featured images of girls who looked close to being or actually underage, and some likely WERE underage, was allowed to exist for an extended peiod of time. Reddit also gave the guy that ran it "a gold-plated bobblehead doll “for making significant contributions to the site.”" reportedly.

• Installed an interim CEO, Ellen Pao, who was there solely to take the blame for some controversial changes like banning some fairly popular if not great subreddits. It was later revealed that wasn't even her decision.

• Ellen Pao was also put under fire for supposedly firing Victoria Taylor, who is a very connected individual and was responsible for many of the site's celebrity/notable people AMAs (Ask Me Anything), including guiding them through the interface and what not so they could capably deliver said AMAs. She was actually fired by Alexis Ohanian, who is one of the founders of Reddit, has worked there on and off, and is currently Executive Chairman from what I can see.

• That time Reddit as a community decided to hold a witchhunt over the Boston Marathon bombings and misidentified the culprit. Not really the admins fault technically, but it could perhaps have been prevented by them.

• The rampant issues with bots, most of Reddit's top posts of the day and their initial comments are entirely reposted content by bots. Very little seems to be done to remove them.

• Also the rampant issues with power users and power moderators. Why exactly can one individual be put in charge of hundreds of semi-popular/popular subreddits?

• In addition to the site redesign, the implementation of things like a chat function on top of the DM function, NFTs, Reddit Premium, different rewards and tiers other than Gold (Reddit Silver used to be a joke for those who didn't want to do Gold), online statuses, avatars, coins, and probably some other stuff I'm forgetting, were all generally unwanted. Most didn't cause that much of a controversy, but I don't know anybody who wouldn't be happier if they were gone.

Probably something else I'm forgetting, but that's what I remember most.