I'm new but I think I have a good grasp of some of the concepts that may help clear some of this up.
Megapixels allow you to capture an incredible level of detail in one click. In the past it we critical that you compose your picture in the viewfinder before you took the picture. Now you have the ability to grab a huge amount of image and the ability to cut/crop/sharpen/shade... etc. all after the fact.
But just as in the days of VHS dubbing - it matters which tape you are using for the initial copy and which you use for the dubbing. Branding matters. Trusting in a brand's quality matters. Sure you can get more megapixels for less money somewhere but if the resulting 'Master' image is crap... you can't make it into art no matter what you do.
It's never just one thing. Great optics on a poor body or used with bad electronics or data capture - will just lead to frustration.
My first digital camera was a used Sony One-shot with a ~1.5 megapixel (or so) level of detail. The colors and optics and software were all top notch. They still are. By today's standards the level of detail is wanting. At such low resolution I learned I had to make sure to compose all my close ups as I took them. For standard printing it looked great. Trying to blow up the kids standing next to the back of the house on Easter where the original includes the whole back of the house (don't ask, I don't know why) left such pixilation of the picture that it was unusable.
If there was only one thing that matters it would be the person taking the picture and what exactly they want from that 'click'. No matter how good the tools are if you don't know how to use them, you will never see what 'could' happen with everything working together to create a real masterpiece.
I'm no authority believe me on the art of photography but I'd like to think that I understand the concept well enough to add intelligently to this thread.
