In my opinion the following:

1. Minority of very vocal users who get angry if you don’t share every point of their world view. Honestly you can just block most of them.
2. Limited active subgroups - There are only a handful of active subs the rest are just dead. Which leads to…
3. Limited content, posts stay in my feed for a week at a time before being replaced. I often block posts I like just because I’m sick of seeing it in my feed.
4. Shitty moderation - mods here are way worse than Reddit.

I’ll be honest I miss old Reddit, Lemmy feels like an apocalyptic wasteland but it’s still better than most alternative. It’s kind of nice I don’t sit and consume content as much as I used to.