All the above are pretty much my experience. Yes, it is very crowded, and hot, but if you know where you are going and what you are doing, you'll be ok. Magic Kingdom is a dead standstill on the 4th. Last year you were literally not allowed to walk down Main Street after around 4pm, as it was 100% gridlock. You exited the park through backstage exits in Tomorrowland and Frontierland. However, if you want to get the most out of the 4th fireworks, here is my suggestion, which I personally think is pretty good. See Magic Kingdom's fireworks on the 3rd, as it is the same show that will be there on the 4th. On the 4th, see MGM's fireworks, as it is one of the only days of the year they show fireworks, and then skip over to Downtown Disney and see their fireworks. There is plenty of time in between MGM's and DTD's to see both. You get in 3 of the 4 shows WDW offers, and it's well worth the effort.