33 new mission trees scattered around the map. New continent (mostly without mission trees, but still fun!)
Steam page: https://steamcommunity.com/sharedfiles/filedetails/?id=1385440355/
Reddit post with release notes: https://www.reddit.com/r/Anbennar/comments/17zwu18/scions_of_sarhal_release/
The anbennar modders are UI wizards. You can turn them off if you want. There is a marginal (barely noticeable, probably not measurable) but theoretically real lag due to the achievement conditions being checked. It’s probably true of base game too.