An optical viewfinder is needed, just like a regular camera. Speed Digital cameras have speed problems in a bunch of areas. The aperture of the lens helps determine how dark it can be before you fail to get a photo. However large apatures take expensive lenses. There are no world record apertures in the digital cameras I've seen.
Most digital cameras take a fair while to process a photo and get ready to make the next photo.
If you always leave ten seconds between snaps this is not a problem, but if you are after action scenes, check the speed to the next photo. You need to get your pictures into a computer, to work on them, and for loading on the internet. File transfer is the most technical thing you do with the camera, and the makers try to shield you from the problems. I like to see the pictures in JPEG format, ready to go on the internet. I would never accept a camera that uses only a proprietary format.