Reddit is
horrible, and I say this as someone with combined ~27k comment karma on two accounts, and years of use. The mods are too happy to delete posts they don't personally approve of (whether they break sub or Reddit rules or not), and I recently got suspended on what appears to me to be a false charge according to the rule itself (a debate on whether some fanfiction should be illegal or not (it shouldn't be) got me suspended - a topic, it is worth noting, is covered by several serious academics). Bitter rant incoming.
The annoying part is that not only does a sub mod get the privilege of deleting posts at will, but there is no appeals process for that, and Reddit doesn't listen to suspension appeals at all.
Aside from that, the downvote/upvote culture is bad (even if I am usually in its favour) and encourages dogpiling and groupthink. Ironically, Reddit with its "don't downvote for disagreement" element of Reddiquette is worse at this than HN with its "downvoting for disagreement is fine" policy.
The site redesign, infinite scroll, a handful of mods controlling many major subs, nonsensical or inconsistent administration and rules, unjust dishing out of punishment, advertisements in the main feed, widespread outrage bait, and endless drama means Reddit is no different to platforms like Twitter where short, witty and possibly fallacious content thrives.
I can count on a hand the number of times I've actually valued information I've obtained from Reddit comments or submissions. That does not justify the amount of time and energy I've poured into the website, which I could have better spent simply not using social media (which Reddit now is). These days, if I had to use social media, I'd pick the Fediverse over Reddit every day of the week. It takes a lot of time to realize that highly upvoted comments (and every comment) is really just "someone's opinion, man" which the current zeitgeist dictates people will agree with.
On Reddit, politics is entertainment (r/PublicFreakout etc.), mocking and hate is central (r/SubredditDrama, r/unpopularopinion), administration is done in the interest of advertisers and personal opinions (phrases such as "weird hill to die on"), and moderation attracts people who would rather bask in the power afforded to them more than people who would rather carefully curate and foster discussion. The one sub which works to its purpose is r/ChangeMyView.
Spending time arguing with random people on the Internet is mentally taxing, very unlikely to achieve a change in opinion of the persons involved or the observers, and terrible for stimulating and interesting discussion. Next time I want to argue a point, I'll get a blog with a comment section, or these days, without one. If my friend told me they were going to register a Reddit account, I'd tell them everything I've just said in this post.