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.

Copying my reply to someone else:

Epic is anti-customer: https://medium.com/@unfoldgames/why-i-turned-down-exclusivity-deal-from-the-epic-store-developer-of-darq-7ee834ed0ac7

Tldr: Kickstarter Game with a lot of interest while in development announces a release date on Steam. After the date announcement they get contacted by Epic saying “we’d love to host your game” for an exclusivity deal.
Dev responds that they would be happy to have their game on Epic but promises were made during crowd funding that it would be available on Steam.
Epic replies that they aren’t interested if it’s not exclusive.

This tells me that

1. Epic is full of shit. "We’d love to have your game, but only if it’s exclusive.
2. Epic doesn’t care about being a better service for its customers. Having the game available on Epic as well is strictly better for Epic’s customers and they easily could have done that. They chose not to.
3. Epic is not interested in actually having to compete with other companies. This would require them to provide a better service in some fashion. They are only interested if they can force people “if you want to purchase this game you have to buy it through us” which is anti-consumer.

Everything but I will focus on the main point of the apps. Selling and managing games.

Steam store page has tags for what genre the game is and user reviews as well as information about system requirements. Plus links to click on to go to the developers and publishers pages to see what else they’ve made. You get plenty of information while it’s still easy on the eyes and digestible.

Managing your games with steam is a breeze. They’re listed down the side and the search is there and quick. Click on a game and get more information about it and see a large install or play button. Scroll down to see info about the latest update or activity from friends playing. Right click to get more information like where it’s installed locally.

Epic, at least when I last used it. Didn’t have user reviews, the page had large widgets for all the information making everything feel clutter while giving you less info about the game. Didn’t have tags and sure it did label the publisher but not the developers and you couldn’t click to see their other works.

Epic’s library management once again large widgets while giving less information. Feels cluttered. Install button is small. At the time I used epic there was not easy way to open install location. You had to go in file explorer yourself and find it.

While I’m on the topic of stores to why do console store pages suck as well compared to steam?! The console is literally sold at a loss and make money by selling you games but their store pages are shit compared to steam.