Google Cardboard was specifically designed to make it easy to try out VR. The cost is low, and virtually any phone you have in your pocket today can power it. Content is even available on the Google Play Store - it can't get any simpler than that.
New Android "Daydream" ready devices (i.e. that meet certain criteria) get an improved VR experience with high performance sensors, high density, low-persistence displays (i.e. high refresh rate).
New Android "Daydream" ready devices (i.e. that meet certain criteria) get an improved VR experience with high performance sensors, high density, low-persistence displays (i.e. high refresh rate).
Depending on the version of cardboard, there may be some size limitations which limit your options. However, if you aren't picky about the hardware phones from 4" all the way to 7" are supported.
Older hardware won't perform admirably, whether it be the SoC (system on a chip), display (resolution as well as sub-pixel arrangement make a huge impact on display quality for VR), or battery life (VR takes a lot of power).
Google Cardboard was Google's way of generating interest for phone powered VR, and is literally just a piece of cardboard (or plastic) and glass lenses. The software is integrated into the Google Play Store, and Google more-or-less put Cardboard out there to see what developers would do with it. Later in 2016, Google will be making their next push forward with Daydream which will be a more modern, well thought through platform.
Even though you may apply the technique to other phones, the prebuilt one is only working well with Nexus 5 because of the screen size, NFC sensor, camera position, and magnetic sensor. However all of these are optional and it'll work as long as your phone screen size is roughly 5 inches.
[Additional Information:] Many phones can fit with minimal modifications to the Cardboard.
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).
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.
The Gear VR does have a USB charging port, but in practice this doesn't extend the play time much. When the phone overheats, it interrupts your game, then instructs you to remove the phone and let it cool off.
This can also increase the movement-to-picture delay, which can cause sensory dissonance in quick movements (when the eyes see a change that doesn't match how far they can sense their head has turned) and therefore (possibly) cause nausea.
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.
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.
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.
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.
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.
The delay between head movement and screen refresh is below 20ms, allowing for low latency refresh rates. This helps to reduce motion sickness, which can be caused by delay from the time you move your head to the time you see the movement.
The Gear VR is compatible with a number of high end Samsung phones, all of which have high quality 1440p Amoled panels. While the PPI varies with the actual phone used, they each offer a good viewing experience.
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.