I'm married to an INTJ, and he can be all of those things, but we also have a great relationship based on mutual understanding and connection. He definitely moved slower than I did in a romantic sense. I am an ENFP though, so I have a tendency to fall fast and hard. He was also slow to fall into favor with my friends and family. He looked aloof most of the time, and then he'd talk and say something that offended half of the people in the room. It's funny, because I think he's this way more the less familiar he is with the people or situation. Like volaine said though, he cracks me up. Some people just aren't ready for his sense of humor, especially since he doesn't ease them in really, just opens up his mouth and lets it fly.
Now, though, my friends and family see him for the devoted, intelligent, loving, and hilarious guy that I knew he was all along. He takes our relationship very seriously, and knows how to joke around and have fun. We have great discussions about science, politics, and all kinds of things that stimulate me mentally, and he's great at planning routes for us when we take trips. He is also great at being objective and helping me work through my problems if I'm feeling a bit overcome with emotions, very even-tempered [except when he gets pissed because of someone's incompetence, haha]. I think that if you can handle him making a few awkward silences happen with some off-color comments, and are willing to give him the space and time he needs to make decisions and think things through, an INTJ can be a fantastic mate. I can't imagine being with anyone else now that I know and love his combination of depth, steadfastness, wit, and devotion.