Lemmy is a great piece of software and works well, although it has some limitations that will be partially improved with version 1.0.

Lemmy also has two major problems, one that isn't related to Lemmy and one that is.

1. The first problem is that Lemmy doesn't handle Activitypub groups managed by Friendica and NodeBB well. It's unable to pick up NodeBB and Friendica posts in the wrong places, so you'll never see any NodeBB or Friendica posts in the community timeline. Fortunately, it handles Piefed communities correctly, because they work with the same logic.
2. The second problem is related to Mastodon: this is effectively a design flaw in Mastodon. In fact, the top posts published by Lemmy are displayed as a message that only contains the title and the link to the message. This is a problem because Mastodon users will always see uninteresting posts and won't want to interact. At the same time, Mastodon users, unless they use apps like Raccoon, will never have clear visibility into Lemmy communities, which are actual Activitypub groups. Only the Raccoon app is able to show Mastodon users and Activitypub group posts as topics, while any other Mastodon application would display them as disaggregated posts within the same continuous stream of all other posts.

These two issues make Lemmy integration with the Fediverse problematic. For example, I'm trying to push the communities of my Lemmy instance feddit.it among the users of my Mastodon instance poliversity.it, and today I can say with some satisfaction that half of the posts published on my Lemmy instance come from Mastodon users who have thus learned to integrate with the Lemmiverse.

Unfortunately, however, almost no other Mastodon instance administrator shows this interest. And unfortunately, mastodon remains the largest community in the Fediverse, the only one that could help Lemmy achieve a greater "network effect"!

This is a shame because mastodon users themselves could benefit positively from the existence of Lemmy communities as Activitypub groups.

So let's hope something happens in the future.