Well, this is what I learn from several INTJs that I knew, online and offline.
At first they seem interesting, smart, and deep. The more I knew them, the more they bore me. They are plain, skeptic, pessimistic, and they seems to keep repeating the same old patterns in everything they do, so it's pretty boring and predictable.
My romantic life in the past with an INTJ was kind of... unchallenging? Like... instead of working together to make the relationship better, he withdrawed, cheated on me, and dating another girl, just to repeat the same cycle with her, and then with another girl and another girl and again and again. He didn't learned anything from his experiences, he just simply end the first cycle, create another cycle, and repeat the same method, only to end up with the same result, over and over.
Other than that, they are okay, I guess. Polite, funny, and assertive.