I've shot with a $40,000 Hasselblad H4D-60 - back when they were new. That's a 60 megapixel camera. I've shot the Canon 1Dx at 18MP and the Canon 5D MKII at 21MP. My main still camera is a Nikon D4s at 16MP currently - and by far - of these 4 cameras - the best images have come out of the Nikon D4s.
Megapixels equate to detail in most cases... but LATITUDE is what makes one camera superior over another. I have a Bachelor's degree in Film Production - specifically cinematography. I learned on film. And really, the difference between a photographer and cinematographer is how many frames per second we capture.
I've not been a fan of digital motion picture cameras until just recently because they lacked one key thing that film just does better... that's dynamic latitude. In cinematography shutter speed is a constant. It's 24 frames per second. So exposure for us has to be adjusted through the ISO of the stock we're shooting with or aperture. Think about putting your digital still camera's shutter at 1/48th of a second and never changing it again. That's what I learned to deal with. LOL. If was frustrating - still can be at times.
A stock's latitude is measured in stops. And regardless of whatever fancy stuff they are going to do to my footage in post production - I always aim for the best possible "normal exposure". Meaning detail across the entire exposure - from the darkest areas of the frame to the lightest. Kodak Vision 3 cinema stock has 15 stops of latitude. I can film someone in shade indoors next to a window and still get color and detail through the window. Ironically, most lenses only have 8 to 10 f-stops.
What makes film look so rich and so beautiful? It's the latitude. The ability to capture realistic, saturated (but not over or under) colors and tones very similar to what our eyes see. Digital has always lagged behind. If I was to film the same scene mentioned above - a person in the shade indoors next to a window - with a top-of-the-line digital motion picture camera you'd not see any color information or detail through the window. It'd just be white.
The problem with digital cameras at first was the size of the sensors. They were smaller than a 35mm negative and therefore they presented more focus - deeper fields of focus - and less ability to capture fine detail. Then there was latitude - the Red One - the first motion picture camera with a 35mm sized sensor - has between 5-7 stops of latitude and captures...