The Oxygen OS 1.0 for OnePlus One does not came as an OTA but we had captured the whole installation guide right here.
OxygenOS is essentially a stock build of Android 5.0.2 Lollipop.
The only changes here to the stock experience are the addition of gestures on the lock screen, a built-in file manager app, and the ability to organize quick toggle settings.
And, you can also set a specific lock screen wallpaper apart from your home screen wallpaper.
Below is a video that shows Oxygen OS in action, but as the reviewer says it would be better to wait for the Official CyanogenMod 12 to see all the surprises.
Even it could be possible that OnePlus will pack more features just to take CyanogenMod down… But, is this really possible???
[Oxygen OS review on OnePlus One by Droid-life]