The very first thing I notice is looks (I'm only human), but I don't go in for one kind of look. I'm attracted to lots of different "types" of guys. There's no physical formula that fits for me when trying to describe my attractions.
And then the personality comes into play, and this is very, very important. Like Wishes, I have had the experience of becoming acquainted with people whose looks were appealing, but lacked a commensurate personality, and the attraction withered; conversely, people who didn't attract notice at first on a purely physical basis can sometimes become beautiful in my eyes due to their charming inner qualities.
If the relationship develops into the physical realm, simpatico sex is essential if the relationship is to continue along those lines. The sex doesn't need to be "hot" or particularly passionate (in fact, I go in for more tender, gentle moods), but the sexual chemistry has to be there if the relationship is to have a physical component.
Lastly, I look for, or at least hope for a similar world-view or values in my partner. The values of the other would not have to mirror my own, but they would have to be ones I could respect (I couldn't date a virulent racist, for example). Compassion, sincerity, and the honoring of the life of the mind are all important aspects I hope to find in someone with whom I am intimate.
