Engadget is one of the first large sites to review the OnePlus One.
For $300, no other phone comes close to what the OnePlus One offers. Not only does it look and feel like a premium device, but it also comes with specs similar to what you'd find in a flagship smartphone. If you want a high-end phone on a budget, look no further.
At this point, you really have to wonder why you would want to shell out twice as much for a Samsung or an HTC. Lack of an SD card slot becomes a moot point with the OnePlus One, as the version with 64 GB of storage is only $349. I obviously haven't used it yet, but from all the information that's out there, the OnePlus One and the Find 7/7a really seem to be the best Android flagships of the year.
I feel like a broken record at this point, but if I were Samsung or HTC, I'd be very, very afraid of these Chinese manufacturers.