I know one well. I get on with him better after understanding MBTI a bit better.
I appreciate the ENTP's ability to grasp ideas, notions, and projects on the grander scale. They can see deep into the core of something. However, they work out the problem from the outside in, rather than ENTJs, who do it from the inside out. ENTPs are bothered by small details; they want to see things happen and move their (usually technical) dream into the physical sphere. They have a tremendous energy for mobilisation and I have a lot of respect for that. However, ENTPs can be one-track minded. If you don't agree with them, that's it. When an ENTP gets started, it's "all your base are belong to us": there are no prisoners. ENTPs can also be horrendously disconnected from people. They view them as a curious and sometimes poorly-functioning components of their master plan. While they can be quite affable, they seem prone to social gaffes and are not always terribly good at dealing with wit or linguistic sleight of hand. Anecdotes are the name of the game.
As an INFP, I can identify with ENTPs. They like people who do not bullshit them. They also dare to dream a dream. The problem is that sometimes it seems like they simply can't relate to anyone. An emotional response in someone else can make their eyes glaze over; someone who dissents and says their plan may genuinely upset people will be met with cold eyes. The thinking seems to be "Why would anyone be upset with this logical plan?" If it makes sense, in the grander scheme of things, to close one area of a business because it's performing poorly, the ENTP is the one to make that decision. The 500 people who lose their jobs are merely a consequence; it's tough, but they have to deal with it: it's for the best. INFPs will also respond with emotions; ENTPs, with logic. "Why don't you understand me!" seems to be the chorus of both.
There is an element which suggests the ENTP carries a lot on his shoulders. I understand that, too. They are deep thinkers and they explore ideas from lots of angles. They become irritated when people question their ideas: "Why are you complaining about that? I already thought about it and decided it wasn't important!" This thinking on behalf of others is very similar to the INFP, who does a lot of feeling on behalf of others. Continuing the business analogy, the INFPs would be the ones to say "But what about the families of those people you've just made redundant? How will they feed their families? How must they all be feeling?" Here is where the ENTP/INFP relationship can turn sour.
If I were the CEO of a business, I would explain my vision to an ENTP, and ask her to implement. If she believed in what she was building, she would not spare herself in realising that goal. Woe betide he who is in her way.
That is how I see the ENTP.