Recs.
Updated
The Gear VR is compatible with certain Samsung phones - the Galaxy S6 and S7 lineups, as well as the Note 4 and Note 5. The Gear VR uses the phone as the display, speaker, and brains - the headset itself is just a head-mount with lenses and controls on the side.
Specs
Pros
Pro Complete freedom of movement thanks to being untethered
Gear VR doesn't have any wires that limit your movement, allowing for complete mobility. The device works when any modern Samsung phone is connected and is controlled with a touch sensitive panel on the side of the headset or through a controller (although some games require the controller).
Pro Priced low to allow anybody to try it
For people that just want to try out VR, the Gear VR brings the barrier to entry way down if you already have a modern high end Samsung phone. It supports the Note 5, Galaxy S6 (edge and edge+ included) and Galaxy S7 (edge included) which are some of the most popular phones from 2015. With a price of just $99 (and also available in bundles for free sometimes), the Gear VR has the ability to bring VR to millions of people.
Pro Consistent development as it is powered by Oculus
Gear VR uses Oculus Mobile SDK and a variant of Oculus Tracker and firmware (Oculus being developed by Facebook and having consistent money backing it).
It comes with Oculus Home, an interface for the Oculus Store, Oculus Cinema, a virtual movie theater and Oculus 360 Videos and Oculus 360 Photos that allow panoramic content playback in a VR setting. These add up to an experience that is already fleshed out with support for many types of media access built in.
Cons
Con Only works with specific Samsung phones
Only supports Galaxy S6, S6 edge, S7, S7 edge, and Note 5. Which limits the available devices and userbase. While Samsung is one of the biggest manufacturers of mobile devices, those that have already bought into a device manufactured by a different company will be out of luck. This can also be exacerbated by the fact that most mobile phones in the states are locked to a two year agreement, so being able to switch to a compatible device is not really an option for those people.
Con Not future-proof
The Gear VR uses a micro-USB port in an age when virtually all phones are releasing with USB-C ports. With no room for an adapter in the casing, this means that the hardware connector will be outdated shortly.
Also, in Fall of 2016 Google is expected to be unveiling 'DayDream' - a standard for mobile VR. Current generation phones aren't expected to make the cut, and because Gear VR is powered by Oculus, it is very likely going to be ineligible for DayDream.
Con Touchpad is finicky
While quite an improvement over Cardboard's simple magnet switch, the touchpad on the side is hard to use. It's easy to input the wrong direction and click when you don't mean to. This makes the Oculus store hard to navigate in VR mode and some games almost impossible to play without a Bluetooth controller.
Con Not as powerful as a desktop PC
Phones currently can't offer the power of a desktop PC. Graphics will not be as crisp as a PC can offer. Also, the experience is prone to lag because of thermal throttling or power saver modes reducing performance.
Con No positional tracking
VR without positional tracking significantly increases user VR sickness. The Gear VR can only track rotation just like Google cardboard. It's ok for short bursts for the most part, but wearing it for extended lengths can cause motion sickness.
Con Blurry text
Even though all of the supported phones all have a 1440p resolution, text can be a bit pixelated (especially near the edge of one's vision) and straight lines end up looking jagged. In games the resolution isn't a problem, as moving around helps blur the images together, but it's noticeable on menus and other static pages.