I still use reddit for some of the niche community-based subs that haven't been replicated here, like What's That Book?, a place where a while bunch of readers and librarians try to help people find books they remember a bit about, but not the title or author. That one is a lot of fun because people are so excited when they get an answer, and because the community is strong enough that most people do get answers. It seems like it would be hard to recreate that experience here. Similar is the Learn Math subreddit, where people ask about things they aren't understanding or can't figure out in their math studies, at pretty much any level, and the community comes up with multiple explanations and thoughts. The variety of questions and the in-depth answers are remarkable.
Generally it just feels a lot smaller and a fair bit more homogenous here. I like this site too, but it kinda feels like what reddit used to be is just gone now.