"You can recognize a person's real character by his wine cup (koso), his purse (kiso), and his anger (kaaso)." (Eruvin 65b)
I don't advise getting drunk, but the point is that to know someone you must test that person in different situations. It's not enough to talk things over. Take the person to different situations and test them out in their midos (how are they when desire for something hits, or are they stingy vs. generous, are they controlling? Are they easy going?)
Excessive anger is a big no-no in marriage. I would avoid an anger prone person like the plague. Also, a big no-no is a controlling person who is rigid and insists on having his or her way.
The Talmud says 3 people cry and are not answered, one of them is he who whose wife rules over him. (Bava Metzia 75) It also says a man should never cast undue fear over his household (Gittin 6b) and that a man must be very careful with troubling his wife, for her tears come quickly. (Bava Metzia 59a)
Bottom line I'm trying to say, is that midos plays a crucial role in marriage, and to research these requires seeing the person in different situations; it's not enough to talk things over.
Obviously, it's important to talk also to find common interests, religious speed, family issues, etc. But as the Talmud says, to find the real character of the person requires seeing them in different/difficult situations.