Pretty much everything really. It’s basically a store and that’s it, no cool features that Steam has. They may have achievements now but not positive. Think it took two years just for them to add a shopping cart. They dump money on developers to release exclusively on Epic instead of spending it making a good experience for customers. No reviews, no forums, no workshop etc.

I grab the free games they offer every couple weeks and use Heroic to play them, not touching their launcher.