Here we go again…
First of all, ignore anything Joseph has to say on the subject.
The majority of Modern Orthodox people are fully shomrei halachah, just like chareidi Jews. Are there those who aren’t? Obviously, just as with any group.
The main difference is in how to relate to the world around us. Modern Orthodoxy does not seek to shelter itself from the outside world. It believes that since we will have to interact with it, it is better to understand it, and know how to deal with it. Chareidi Judaism believes it’s better to shield yourself from the world, and not expose yourself to the temptations that are out there. The end result is that chareidim are “safer” earlier on, but can have a hard time adjusting when the exposure eventually comes. MO may have some who give in to the temptations earlier on, but later are better at dealing with the world because they are prepared for it.
Another difference is the view on secular knowledge. Chareidi Judaism is mostly against studying anything other than Torah, with the possible exception of studying to earn a living. MO believe that since all knowledge comes from Hashem, and has its source in the Torah, it is worth studying. Even if it won’t help you learn Gemarah, it still can help you relate to the world that Hashem created, and appreciate it better.
One more difference is how to view Israel. That’s been discussed ad nauseam here, and I don’t see a need to go into details.