On the contrary, the Turbo's screen is pretty darn good. The hot new Galaxy S7 and S7 Edge, for example, has exactly the same 1440 x 2560 screen resolution. Apple's so-called "retina" display for the iPhone 6 is a mere 1080 x 1920. The purpose-built VR headset Oculus Rift's resolution is actually slightly less
than the Turbo.
The issue is that any
tiny handheld screen just doesn't look great when magnified to appear the size of your living room. The pixel tiling is going to be visible. By my very casual estimate, you might need a resolution over 6000 pixels wide per eye
to exceed the ability of your eye to see the pixels -- implying a screen about 12,000 pixels wide and correspondingly high: roughly 20 times current smartphone resolution.
That's my two cents. Perhaps someone more in tune with the state of the art of VR hardware can fill us in on where the industry is headed in this regard.
In the mean time, the Cardboard platform is a fun and cheap way to figure out what else you love or hate about the VR experience. Content sucks? Sound is not integrated with head motion? Sensor lag? Navigation and controls? Walking into walls? Then get into a store and see if the expensive headsets solve enough of the problem to be worth it to you.
There are nicer Cardboard viewers in terms of build quality, comfort, and materials. You can find Turbo-compatible ones on Amazon and on Google's Cardboard
site. But since the weakness is the screen itself, which you supply, you're not going to improve the visual quality much at all. The lenses that came with your generic Cardboard viewer are essentially as good as you'll get.