Science Fact: Women can find entirely different facial features attractive, depending on the kind of relationship they're looking for. Furthermore, they have a much broader definition of "attractive" than men do.
Explanation: Guys are pretty consistent when it comes to attraction. If you showed them pictures of women and asked them which ones they'd want to have romantic sexytimes with, they would furrow their brows, think super-hard, and be like "Ummmm... the hot ones." If you held up the same exact pictures and asked them which women they'd want to date, they would look at you blankly, like you were trying to trick them. "The... the hot ones," they would offer, confusedly. "QUESTION MARK?" they would think to themselves.
If you got a bunch of girls in the room to answer these questions, you would need spreadsheet software.
The Science: Okay, so we've already brought up that girls (and guys) will find you more physically attractive if they believe you have positive traits, like honesty or spidey-sense. But it gets more complicated than that, because it turns out that guys and girls aren't even working from the same definitions. If you simply showed people pictures of humans, and asked the guys to pick out the hot girls... well, they would probably be pretty exasperated with you by this point. ("Oh my God, the hot ones are hot! What is wrong with you??") "Hot" has a pretty obvious definition for them—seductive, thin, confident—and they practically don't even know how to vocalize it because it's so universal. But if you asked the girls to pick out which guys are hot, you would get a lot of responses like "I like the one who looks like a mop!" and "You know who's attractive? The unattractive one." Massive studies tell us that women have a much more inclusive definition here—one can find a guy perfectly attractive while another thinks he is a swamp creature.
On top of that, is also depends on what kind of relationship the women are after. If you ask them which guy is desirable for a short-term fling, they'll pick the strapping, square-jawed quarterback, Lance Musclebeard, who is constantly expelling testosterone out of every orifice like a lawn sprinkler. But they will find those exact same physical features less desirable if they're specifically looking for a long-term, emotional relationship, in which case they'll prefer more feminine, less testosteroney features (e.g. fuller lips, a rounder face).
So What Should I Do About It?
Basically, play to your strengths. Guys who look like Captain America can fling woo at whatever woman they want and make them weak in the knees, and they can topple them right over with one smoldering glance, or, failing that, by throwing a shield at them. But that doesn't mean that the rest of us, with our roundy faces and mopey demeanors, are doomed to wander the terrible Earth alone forever. It just means we have to work with what we've got—features that women associate with faithfulness, warmer personalities, and better parenting. Thanks to how forgiving girls are with their definitions of hotness, you don't need to be a vigorous Adonis—you will, however, have more success with sentiments like "I care about you as a person" than "Hey hot lips, meet me in the broom closet."