Having worked one of the top auto manufacturer websites from top to bottom, MPG and Seating are the next two things you need to add. Particularly right now, MPG is top of mind as gas prices are skyrocketing. And seating is always important. It helps to know whether you'll be able to fit your entire family.

Next comes trunk space and safety ratings. Can I fit what I need to given my particular lifestyle? Will I have a better chance of survival in a crash?

Awards help as well, such as Motor Trend or J.D. Powers. Those factor well into the decision-making.

Funny enough, random things like number of cup holders is a deciding factor some people. Will there be enough cup holders for everyone's drinks?

Regarding the interface, I think it would be particularly awesome if filtering and display updates worked using this jQuery isotope plugin: http://isotope.metafizzy.co/demos/filtering.html