For a while it seemed like more megapixels where the thing to have. If a six megapixel sensor was good, then twelve must be better, right? Pixel density went up, image quality went down. It's just not that easy.
Then there's the sensor size debate. A bigger sensor, one even approaching the magic (and odd) 35mm format, must be better than a smaller sensor. This is true to some degree because the pixel density goes down. That's true now but I'm sure that will change. Pixel densities are starting to creep up there.
Now we're into ISO silliness with lofty numbers like 25,600. I'm not going to take the time to calculate exactly where you could use an ISO like that. In daylight you would need a ridiculously high shutter speed and a ridiculously small aperture. You would need to be in a hell of a dark place, shooting available light, without a tripod, to make this a viable number.
Most digital cameras shoot well between ISO 100 and 200, even cell phone cameras. Most cameras are good at 400, even 800. Above that you're into bragging rights. When you hit ISO's in four digits it gets hard to see what you're aiming at and even harder for the camera to auto-focus.
More of anything is not always better. There's a tipping point. What makes this interesting is that we should know better, or at least those with film experience should. Higher speed films had lower image quality. That's massively over-simplifying the science here, but true. Physics didn't change, just the recording medium. Image quality is what matters.
When I read a camera review I look for image quality up to ISO 800. Above that falls into "that's nice" territory. The majority of my images are for the web, not print. I can lose a little image quality since I'm not making large prints. However, if image quality is of ultimate importance, I'm heading for medium format cameras. It still comes down to resolving power. Not much as changed since film days: bigger film hold details better than smaller film.
The point is there is no one perfect camera for every possible purpose. It's pretty hard to find a bad camera these days. The reviews are very helpful - if you know what they are talking about and it applies to you. There's great images out there taken with not so great cameras.
So, don't get thrown off by all the numbers. Get a camera that's good for you and enjoy.
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