All of these covers are awesome examples of great artistry. They all have similar themes, one of them being circles and straight lines. Even the helmets of the various armors seem to all obey the same contour lines. The color schemes of each cover are limited to a palette of around four colors, different shades not included, allowing for very simple eye flow. The smaller circles surrounding the head also provide an invisible base line to follow with the big white circle in the center.
Font choice is also prominent, focusing on all capital letters and placing the title and credits all in the same place of all five covers, completing the idea of this being a mini-series. The off centered text also helps and gives a nice conformity across all the text, retail bar codes not included.
FUN FACT: The forth cover isn't actually a suit of armor worn by Tony Stark. It is actually a suit of armor for Pepper Potts when she briefly becomes the super hero Rescue.