I think the following is the bare minimum to compete with Steam at this point: 1. Store with discoverability, 2. A functional cart feature at launch 3. A wishlist with notifications for discount 4. Relatively high download speeds (500Mbps at least) 5. Friends list and activity feed 6. Achievements 7. An equivalent to steam input API 8. Regional pricing with robust payment options 9. Development/Beta build distribution as easy as steam. 10. A useful in-game overlay with at least performance metrics. optionally a web browser and notes.
All of the competition has missed either one or more of the features, making them feel like only a cash grab trying to avoid Valve's cut for providing these features.
Missing a few things there: Reviews and working on linux, for example.
I guess everyone gets different value from different features but I for one would not even notice if Steam removed the overlay, achievements, activity feed, input API or beta distribution. It all seems like bloat to me.
Those features are important but I think the key things are the actual games and friends. You cannot start with empty catalog and you also cannot start with older games people already own on Steam. You also need friends to be there on day 1 for multiplayer.