Yup. It is totally unwatchable. Just looks like mush and nothing can fix it. No matter what you do it just looks terrible.
Now if you believe that statement then that is how rumors and stereotypes start. I completely made up everything I wrote above. However, if I didn't put this disclaimer below it then everyone would have run with my statement. They would have said "Even an established Vizio Honk like me thinks it can't upscale". Everyone would keep stating that until something that was untrue became accepted as true.
The reality is that you shouldn't believe anything anyone says unless they demonstrate it with clear evidence or at least verifiable data. Upscaling is the only thing that RTINGS.com tested but really didn't provide any proof at all. They just drew a conclusion and left it at that. Their pictures they provided don't even backup their own conclusion even though they intentionally altered the settings(Turned off local dimming) to make the Vizio look worse.
If you watch low quality video with the TV and the out of the box settings you will be disappointed. Those settings are not good especially for overly compressed material. I have listed some settings below that will improve your low quality watching greatly with the new P-series. If you try these settings then it will look like any other TV even for low quality stuff.
Backlight = something less than 77 (If you go too high with backlight it will stop the pulsing that it does and just "Hold" the backlight on. That makes motion more prone to ghosting)
Brightness = Default (Don't touch this at all or you are the one to blame for the picture quality issues that arise.)
Contrast = Default (Don't touch this at all or you are the one to blame for the picture quality issues that arise.)
Color = 50 or 51 (You really have to be careful with this setting. It can cause serious color issues even with moderate increases in value)
Sharpness = 8 to 14 (Don't go too high or too low. Going too low is just as bad as going too high. Use the noise reduction controls instead of going too low)
Black Detail = Off (It doesn't work well on the P-series)
Active LED Zones = On (With the latest firmware this should always be left on.)
Clear Action = Off (No need for this with regular TV content. This is a Computer specific setting)
Reduce Signal Noise = Off (Unless you have content that has noise in it and you want to remove it. Honestly, my recommendation is to never turn it on.)
Reduce Block Noise = Off (Turn this to low if you use 8 for sharpness but you still want it to blur the macro blocks more. If you want even more blurring then just use High or Medium.)
Game Low Latency = On (Ok here is where everyone loses their *****.)
I have been testing all of the settings trying to figure out what works and what doesn't with this TV. I have come to the conclusion based on my testing that something in the processing just isn't right. I am not sure if it is in the motion interpolation settings or something else. However, when I turn on Game Low Latency the macro blocks from compression seem less noticeable. It isn't that they disappear. It just seems like they are less noticeable.
I know this is sacrilege. The common thought is that processing always helps with low quality content. However, it could do harm just as easily. In the case of the P-series my testing indicated that it was doing exactly that.
The nice thing is that Game Low Latency doesn't disable the sharpness or Reduce Noise settings at all. You can still use those but it will disable the motion controls.
I found that the motion controls were causing uneven motion and they really weren't helping with regular broadcast content except for scrolling text. They help tremendously with a computer but they aren't helping with regular TV content. The motion controls also cause lip sync issues. If the video delay goes from approximately 17 ms to over 100 ms and the audio doesn't change then you will definitely get lip sync issues.
You can't touch the individual brightness color controls at all. If you do then everything I have stated above goes out the window. You will cause posterization in some content that appears like really bad mosquito noise. If you insist on doing that then I can guarantee that your experience with low quality content will not be good in certain cases.
Give GLL = On a try with the other settings I suggested. I think you will be surprised. Just don't think that any TV can totally get rid of compression artifacts without severely compromising the resolution and detail of the content. Garbage in equals Garbage out.