Ok, we start out with an original image. Properly exposed, not too dark or too light, lots of detail in the dress, while maintaining the details in the shadows, skin tones look accurate. This is what you're looking for.
The second image is completely blown out, almost all the detail in the dress is lost. Brides pay thousands of dollars for a wedding dress, if you can't capture the detail of it, what's the difference between a burnt out wedding dress and a cotton bed sheet?
The third image is all about shadows. They give any image definition. In this shot the blacks were completely lost and her head seems to blend in with the background giving the image a 2D effect. Again, this is NOT what you want.
Image #6: Hahahaha I love this one. I call this the "kind of sorta almost in focus" lol! If you're browsing through websites checking out any professional photographers work, it should be TACK SHARP and in focus in the right places. For example when shooting a head shot or portrait, 99% of the time any head shot should be focused on the eyes. Not the nose...eyebrows...top of their head...shoulder...or collar. Any classic portrait is about the eyes. There are always exceptions to the rule though and when you see an experienced photographer break those rules, they are intentional and obvious.
Image 8. Over-sharpening. This causes the images to look unnatural and cartoonish. A little bit of sharpening can add a lot of punch to an image though.
So that's it! That's my opinion on what to look for and what to avoid when searching out a qualified wedding photographer. I hope it helps!