OxygenOS based on Android 6.0.1 Marshmallow.
2.2GHz quad-core Qualcomm Snapdragon 820 processor.
Adreno 530.
6GB LPDDR4 RAM.
64GB internal storage.
5.5in full-HD Optic AMOLED screen ( 1920x1080, 401ppi) , Gorilla Glass 4.
16Mp rear camera, f/2.0 aperture, 4K video/120fps slo-mo at 720p.
8Mp front camera.
Now these are the key features required In any smart phone.
And you are getting all these features beyond your own expectations at a different level with a suitable price and quality as compared to other phones.
You should not think to buy it when your pockets allows.