It depends. Some of them are likeable and pleasant, but there are many who have big egos, a kind of intellectual fancy stuff to them, and alot of arrogance, as if they are superior to anybody.
They are very smart almost always...but also, surprinsingly stupid in many aspects. I always have this image in my mind: if a INTJ is thinking on hiw own, he can make some awful mistakes, but let a INFJ to stand by him, and they can make a great team.
This of course, if the INTJ "accepts" a INFJ contribution, because usualy they believe themselfs to be the supreme intellectual authority.
I have a INTJ friend from basketball. When we begin to talk, he always starts from the upper position, when we finish to talk, he becomes more mild and humble.
As for comparation with ENTJs...let me tell you the most surprising aspect of this. I've never seen one single ENTJ to be arrogant: they are simple, straight-forward, democratic in manners, sometimes very modest, and rarely they try to act superior, but when they do it, you can not take it seriously, its more laughable then offensive.
But with INTJs...their arrogance is real and it can be felt, and of course its very unpleasant. They can be very proud people.
Again, not all of them. Some of them can be actualy very modest.