The most important element of design to me is color. More than anything else, it can define the mood of the piece and determines what emotion is transmitted to the audience. While I personally prefer natural and/or cold colors in a design, also the lack of color (aka black, white, grey) attracts my attention since it can give the pictured object more weigh and importance.
To continue, one of my favorite things to look at in designs, are lines. I've always liked to look at and create line-art. I like pictures that are solely established trough one single line, but it also gives me gratification to look at realistically laid out designs, with a twist of an unnatural outlining. In addition I enjoy watercolors without any well defined lines but, in contrast to the prior statements, mostly smudgy outlines.
Last but not least, I've realized that I do mostly enjoy natural shapes, but at times I appreciate the unnatural and geometrical shapes (as well as lines) that give a twist to an basically realistic object. I find it highly enjoyable to figure out what components of an unnatural design give me the familiarity that I would usually receive from a realistically shaped object only.