Others have covered most.

For me the one killer feature is grouping of duplicate articles over multiple instances into one post, with comments from all instances listed therein.

This takes away the ghost town feeling of Lemmy, and the frustration of seeing the same post multiple times while scrolling.

The one bad thing is we can’t upload images to posts or comments, so it’s several steps forward, one step backwards.

Edit: you can post images if you’re using Summit on Android, just can’t seem to do it via the PWA / Web version.