well that's what wikipedia says anyway formalism is the citique of work on the formal quality for example in music formalism would look at the melody for us Photography types its depth of field hue saturation grain colour texture light. Our eyes automatically like rhythms and patterns, along with balance of colours and light, so images which have good formal qualities would automatically be more popular.
below are some examples of different formal qualities in images at different end of the spectrum
Depth of Field
in the top image taken by me at york minster a while ago the entire building is in focus, the second doesn't need to all be in focus so having a bigger depth of field keeps just the important stuff clear, in this case it was Sarah's Hair while the reflection in the mirror was blurred
Composition having your main subject in certain places within your image can considerably change how attractive to the eye it is, there are lots of rules on whats pleasing and whats not, but sometimes breaking those rules can work just as well!
Hue
Hue is looking at the colours within an image, for example adding a blue hue can make a picture appear cooler and orange tones can warm an image up
http://better-photography.com/tips-great-fall-photography/
saturation refers to how much colour is in the image so desaturating on an image can make it look older and can give a classic timeless look
turning up the saturation can highlight certain parts of an image, for example if just the red was extenuated it would draw attention to those bits of the image
grain
grain is sometimes considered a bad thing in images, but can sometimes give a nice softness to an image
colour
colour is an aspect that we take for granted but sometimes the absence of colour can make more of an impact
Texture
Texture is a bit like grain, it can be a useful tool for making new items looking old, it can also add to the aesthetics of an image making it more pleasing to the eye if something in the image has a natural texture.
light is one of the most important aspects we think about as photographers, everything from if we have enough of it, is there too much, where is it, whats the quality of it, can we control it, the amount of light can make a picture
This image was at a wedding and the DJ light had hit my lens at the perfect angle to make the lines of light across the frame, it was unintentional as when i was composing the shot the light wasn't in the same place, but I absolutely loved the outcome
This shot was taken a couple of seconds later and was the shot I was aiming to compose the light in the background makes the silhouettes stronger and the lack of light highlights the things that really matter, the couple