There is a lot of science (well, let's say there is a lot of "science") about mate choice, what's attractive to whom and what that means for us as a species. For example, in general we, all of us humans, prefer healthy, fertile, socially successful, rich people whose immune systems differ from our own (see Red Queen Hypothesis).
One guy, Geoffrey Miller, proposes that the profligacy of the human cortex (the "thinking" part of the human brain) is due to women's evolutionary preference for the smart ones, the creative ones, the musical and lyrical ones. Of course he also thinks women selected for sexually competent partners (i.e., those who made them have orgasms) and he spends a lot of time talking about penetration, when we all know by now that only a third of women are reliably orgasmic from penetration, another third are sometimes orgasmic from penetration, and the remaining third are never or almost never orgasmic from penetration. It has little to do with partner competence. So. Meh.
Anyway, in the western industrialized world we like a good sense of humor and we like it when we feel that someone respects and understands us. We like it when people share our values, not particularly because it makes evolutionary sense, but it's a hell of a lot easier to live with someone for most of your life when you don't think they're morally inferior to you. We like people who are about as smart as we are - again, not really for evolutionary benefit (or else we'd all like the smartest people and any woman with a brain knows THAT'S not how it works) but because it's nice to be with someone who sees the world in approximately the same way you do.
Oh, one more thing: "S/he has to have a good personality."
Personality, for those who are interested, is a collection of traits that are more or less stable across a person's lifespan. The most widely used framework for thinking about personality is the Big 5: Openness to Experience, Agreeableness, Conscientiousness, Extraversion, and Neuroticism.
What makes a "good" personality? Well it turns out most people want partners who are more Conscientious, Extraverted, and Agreeable than we are, but about as Open to Experience as we are, and less Neurotic. So the "best" personality, it seems, is organized and reliable, sociable, has difficulty expressing irritation with others, and tends not to worry too much about things.
So there you have it: "good personality" means laid back, likes to hang out with friends and have a good time, does what they say they're going to do. It's all the fodder of online dating profiles.
For those of you now in need of reassurance that your desires are normal, don't worry, you are not alone. I too DON'T want someone laid back who likes to have a good time. I would have no idea what to do with that person. I'd rather find someone as intense, driven, anxious, moody, introverted, and misanthropic as I am, so we can order in, drink excellent beer, and watch Netflix when we're not doing our jobs, which are defining features of who we are and take up huge portions of our lives.
Technically I think this means I - and you, out there, needing reassurance - have a "bad" personality.
What a relief! I'm released from the drudgery of giving all the perfectly nice people a try; I can cull right down to the nutty-enough-but-not-too-nutty.
I wonder if anyone has ever written a book on how to meet someone Neurotic and disAgreeable. Maybe I should. Oh, maybe YOU should! That would be awesome. A dating how-to for the curmudgeonly. And every copy will be bought online because none of us can be bothered going to a bookstore and being around people.