The more I interact with other digital stores, both on PC and console, the more I love the Steam platform. It is so far and above any other store, only gog.com comes close imo.
I love the sheer range of games you have available to you, I love the sales and the fact you can buy Steam keys from 3rd party resellers to get great deals as well.
I love that you can easily go to the reviews section, not just to check if people think the game is good but reading the recent reviews can be a great way to find out if a game has gotten better or worse. Some games launch in a terrible state, Chrono trigger for example, and if you just went by "professional" reviews you would never know that the developers put the time in to fix the issues and is now a great pot on PC. Like wise you might find out if an older game has issues with newer OS or latest drivers you might have to work around.
I love the user forums where you can go for help or just general information on the game. I love the community portal for each games that lets you access guides or forums easily in game via steam overlay. Games are getting much better at providing options like borderless windowed mode but there are still a lot of games that don't like it if you alt-tab to a browser.
I really like Steam achievements, not in every game but I find they make me think about the game in different ways some times. I have even rebought games I have on other stores to get access to Steam achievements. Hell, I even like the trading cards and badges.
Steam input is amazing, enough said.
All in all I simply find Steam to be the standard I hold every other store to and like I said I feel like only gog.com really approaches it. For Christ's sake the Epic store still does not have a shopping basket! Browsing the xbox store you will find games, especially older games, that wont even have a trailer available to watch before you buy a game.
I will of course grab the free games from Epic and I will buy older titles on gog.com but given the choice I nearly always buy on Steam for all the features it provides.