What stood out the most to me was when everybody left Reddit and came to Lemmy that everyone helped each other to get settled into Lemmy and the Fediverse - at least where I settled. Knowledge was passed down. More tech savy users answered the questions of new users patiently. Everybody was (and still is) polite in general and it is a pleasure to participate in such an enviroment.
I experienced (and I still do) much more “adult” behaviour within Lemmy, compared to Reddit. I barely have to downvote comments due to bad/ malicious behavior. I think I have had to downvote 3 times within the last 8 months - and one downvote was dedicated to a bot which summarized some news content wrong. Here you can have nice discussions and most comments actually contribute. Less “This”-comments.
I like that Lemmy in general is more left leaning, and also more tech savy. Also, I experienced less gatekeeping than on Reddit - at least, within my home instance. Your experience, however, may differ.