Hi,
being a n00b here, and in the whole MBTI thing in general, I don't know too much about ENTJs and what makes them tick. In spite of this, I have a few suspicions about the type, since I believe that both my gf and one of my best friends are ENTJs. Here's my two cents.
First of all, they can both be horribly arrogant, and often in a very blunt manner. They're absolutely delighted with who they are and what they represent - ambition, intellect, initiative, organisational skills, social skills (charm), a good sense of humour, and so forth. However, they both look down on anyone who is not like them. Especially when I speak to them in private, their judgment of others is often so harsh I sometimes find it appalling. Though I often share and, up to a certain extent, appreciate their disdain for those who are considered 'stupid', I tend to be less open about it.
Second of all, they're both horribly intelligent and disciplined. And when I say horribly, I mean it. Never have I seen such a brilliant combination of intellect, initiative and organisation as in these two. They're not afraid of anything, it often seems.
Third of all, they both have a mild tendency towards substance abuse, my gf being a heavy smoker and my friend being quite a heavy drinker at times, getting pissed off by the absence of beer in his immediate vicinity. What's strange though is that when they want to quit smoking or drinking, they just do. They can simply stop for months on end out of the blue - I cannot. When I've been without a cigarette for more than 12 hours, I go insane. They do pick it up again, however, in the end. But only after they've passed their tests or something like that. Weird.
So, the ENTJ, in my opinion, is fun-loving, arrogant, smart and disciplined. The upside to them ruling the world would be that everything would be quite neatly organized - no obnoxious politicking, no slow decision-making, just making sure things work and function. The downside to them ruling the world would be that a lot of people would be left to fend for themselves, especially if someone has problems because of their own faults. There's no second chances in the ENTJ world. They're very cruel, that way.