Valve has put a lot of time and effort into its SteamVR program, and its partnership with HTC on the Vive headset. While headset hardware can set the platform apart from the Oculus to a certain degree, the idea of a headset with video playing is a pretty solved problem at this point, Where Valve can really set itself apart is in controller hardware, something that has been a bit of an overall loss in the industry.
At Valve's Steam Dev Days, an event which does not allow press but does allow smartphones and Twitter, the company showed off new controller hardware which seems to address the biggest issue with other controllers, including previous SteamVR controllers, the inability to open your hands. It also eliminates the grip buttons on the side of the previous model, instead sensing grip based on overall hand movement.
A good controller could be the feature that sets one platform apart from the others, or at least encourages sales. It is less than likely that a single accessory will determine the fate of a platform, but a controller is the thing that makes VR fun or a chore. Obviously we have not yet interacted with this new prototype, but seeing video of the controller in action is encouraging.
Of course, Valve is not known for their hardware, especially controllers. When they were still trying to make SteamOS work, the controllers were bad enough that the company decided to design the platform to allow for Xbox controllers instead. Hopefully they learned their lessons from the overall disaster that SteamOS was, and have applied those lessons to SteamVR and this new prototype controller.