Most of July is very crowded. The exception is July 4 and days surrounding it which are extremely crowded. July is extremely hot and usually daily showers off and on in the afternoon to evening. Though that July 4 time comes close, the two weeks surrounding Easter are even more crowded. One way to describe Easter time: its noon, you have just entered MK and you are at the base of Main Street looking down the street toward the castle; you do not see Main Street, you do not see the sidewalks, all you see is a sea of bobbing heads next to each other. Crowds can get so thick at MK that it can take 30 minutes or more to walk from Splash Mountain to Space Mountain. Popular rides get 2 hour and usually longer wait times most of the day and evening and some like Test Track and Soarin' get to three hours. Even things like the Treehouse get greater than 60 minute lines. Fastpasses for popular rides run out for the entire day and evening by noon. At least MK, on some days, may close to new entries for a few hours because of overcrowding. If weather is nice (and most often it is -- warm days, pleasant evenings, rain showers happen more often than not when you are sleeping at night), waterparks will fill to capacity by 11 to 11:30 and if you do not arrive early in the morning you can essentially forget about getting any chairs at the waterparks. You must have ressies for dinner if you want any sit-down restaurant and those should be made long in advance. True story: while in line to check in at Crystal Palace one year on the Thursday before Easter, a family of four was in front of us, without a ressie, and asked if they could get in at any time; the CM, after running through his computer screen for a while, finally said, "Tuesday at 8:45." At usual eating times even the counter service restaurants can have 40 minute and longer lines.
I do not recommend Easter to any new visitor nor to any repeat visitor who has a desire to do every attraction. However, this is what we have learned having done it many times and gone with an attitude that if get on something good, if not, no matter:
1. Make all your dinner ressies well in advance. Sometimes you get things by calling the day before while you are there often because cancellations start to happen. Thus, attempts to change while there can sometimes be successful.
2. If you really want to do waterparks, plan to go early in the morning, or wait until late afternoon -- they get to capacity but then crowds start disappearing about 3.
3. Early mornings at opening time for a park can be a time to do some of the rides without long lines. Note they will often dispense with early entry for resort guests at the parks during this time and just open them all to everyone an hour earlier than usual. Also use fastpasses as much as possible after the early morning.
4. The most crowded times at the parks are usually between 10 and 3:30. For parks other than AK, you can get some respite between 3:30 and about 7:30 (parks other than AK stay open late) and then crowds return again both for rides and night time activities. Even at AK, a number of things may open up after 5. At MK, everything has long lines at 10:30, but late afternoon/early evening, you will find many (other than mountains, Pooh, Peter Pan, Jungle Ride) may have much shorter lines -- in other words if it looks too long in the morning come back later. The same is true at Epcot for other than Soarin, Test Track, and Mars; for example, Spaceship Earth can get hour and longer lines in the morning because arriving crowds flock right to it, but by 3:30 it can be walk-on. At MGM, Mermaid, RnR, Tower, are packed all day but others can slim down in late afternooon/early evening.
5. Lines for even popular rides can sometimes decrease to bearable (e.g., 30 to 45 minutes) during parades and, at MGM, during first Fantasmic.
6. If you must see parades, consider what you are going to do. For the daily at MK, people actually start occupying prime viewing areas 2 hours before the parade begins. We just wait until last minute, and find something with some elevation (like Town Square steps) and look over crowds. There are usually two nightly parades at MK and the second, late one is always much less crowded than first.
7. If you are not going to do a parade but are going to be in a park, make sure you get to wherever you desire to be during the parade at least 40 minutes before the parade because if you wait too long, it may be impossible to walk to where you want to be.
8. There are usually two Fantasmics at night. For the first one, you may not get in unless you line up an hour or more beforehand. For second one, you can usually walk-in at the last minute and still get seats.
9. If you want to see any stage shows in MGM, AK, plan to arrive 45 minutes or more beforehand (and sometimes that is not even enough).
10. We have found the "lightest" days (and all that means is that the crowd is not quite as huge as other days) for Epcot, AK and MGM are actually Saturday and Easter Sunday, that partly has to do with those are prime moving days for many and because people flock to MK particularly on Sunday. MK is just overwhelmingly crowded everyday with Saturday through Tuesday after Easter the worst.
11. There is absolutely nothing that goes on at MK on Easter Sunday that you cannot see other days of the week. Despite that, huge numbers go there on Sunday believing otherwise. Avoid it if possible. Disney does not treat Easter like Christmas. You get some extra decorations, and some easter egg hunts and crafts at the resorts with a visit from the bunny on Sunday (which activities themselves are unbearably crowded). There are also some resort restaurants with Easter brunches which you must reserve well in advance. Otherwise, it is treated like any other spring break week.
Same here.
I had warned my BIL about this a couple years ago and he came back and said that he may never go again. And he had been there numerous time before. I'm sure once the shock wares off he will be fine. Kind of like having a baby! 
