OkCupid was good at that. It was unique though.

The GP liked OkCupid (until it was bought by match.com and ruined), so I think the GP is referring to the kind of corporate-monetising and "it's out of your hands" matching done everywhere else as the road to hell, with OkCupid's method being significantly different.

I believe the key to OkCupid wasn't just that it asked what you want your match to answer. I believe the main key was that OkCupid did not choose all the questions; the questions themselves were quite free-form, provided by users, and ranked by a statistical method to sift the most helpful questions. So they reflected real-life interesting factors that really affect people's compatibility, instead of what dating site designers think you should be asked.

And there were simply a lot of questions with which to build a rich picture without a prescribed schema. It was fun and thought-provoking to answer them because the system generally seemed to promote good questions. You felt like answering them revealed something useful that you wouldn't have thought of asking about. It promoted curiosity, and it seemed worth it to find out what non-obvious matching outcomes would look like.

Essentially, OkCupid's matching questions ended up being refeshingly honest and effective, it uncovered interesting characteristics that didn't seem obvious until they did, it had an air of curiosity rather than commercialisation, and it gave people a chance to find each other who would never had met under the schemas used by other sites.

And because you could see how well you matched with people and on which general axes ("selfishness", "inquisitivness", "religiousness" etc), and some questions, you were free to think about and reconsider your answers. They also gave you talking points.

For example, an emergent line of questions was about polyamory. Most sites don't ask, with the result that some kinds of poly people never find compatible people on those sites. Or, "are you bi" may be asked, but OkCupid's emergent questions would end up asking what kind of bi, the kind who must be with different people, or the kind who are gender-indifferent (and only want one person)? Those are distinct compatibility groups. Maybe you yourself only want one partner, but don't mind your partner snuggling/kissing/everything other people. Or you do mind, a lot. Or, are you asexual, or mostly so, but still want romance in your life? What kind of romance anyway, what does that mean for you in practice? These sorts of questions make a big difference to some people.

Then there were useful non-sexuality things such (making these up to give a flavor) as how often do you like to go on holidays, when was your last camping trip, what is your idea of a good Sunday morning, how tidy do you like your home to be, would you support a partner who wanted to go to college if you had to pay, have you lent money to a friend then been happy to write it off, which boardgames are best, should cheese on toast include onions, what's a good bedtime, do you support intervention in Afghanistan, would you bend the knee, spliffs, brownies or no drugs, how many children would you prefer, what about adoption, is black the only proper color for clothes, vi or emacs, rust love it or hate it, etc. So much that other sites miss.