It will be extremely crowded at all parks. Early morning is best chance to hit some things in any park before the huge crowds start. Some thoughts:
Fast passes: though they become a necessity, you should assume that fast passes will run out by noon for the entire day for the more popular rides and attractions.
Restaurants: You must make buffet and sit down restaurant reservations for dinner well in advance, and wise to do so 180 days out for character meals. True story: on the Thursday before Easter, we were at Crystal Palace in line to sign in for a 6 ressie and people in front of us had no ressie. They asked for when anything would be available. The CM checked the computer for a long time and then looked up and said, "Tuesday at 8:45." If you do not have reservations for park restaurants you will not eat. Also if you plan to eat at the counter service restaurants expect long lines during any normal eating times; the line can be up to 45 minutes and when you get food you may find nowhere to sit.
Parking: if you intend to drive to any park be aware that lots can fill particularly at MK. That can be the first form of closure at MK where they are not letting anyone in anymore for parking.
MK: Standby lines for popular rides can get to 2 1/2 hours, they can sometimes decrease significantly during a parade. Starting about 9:30 everything has long lines even Treehouse. Beginning about 4 and ending about 7:30 many things can get much more reasonable lines, e.g., Pirates which may have a 90 minute line at 11 may be no more than 10-15 minutes at 4 and that is true for a number of things except the mountains, Pooh, Peter Pan, and Dumbo which seldom ever let up. After 7:30 huge crowds return except for some relief for lines at rides during the nightly parades and then about an hour before closing if closing is at midnight. Between 9:30 and 3:30 and for a while after 7 the park itself is difficult to walk through because street crowds are so thick. MK is extremely crowded everyday but its even worse two days are Easter and the day after. Everyone goes there on Easter under the belief that something special happens at MK on Easter that does not happen the other days of the week. It doesn't. Nothing goes on there on Easter that you cannot see the other days of the week. For parades if you must see them, recommend that you just wait until shortly before they happen and find an elevated spot (like stairs in the Town Hall area). Trying to go "early" to reserve a good curbside spot means at Easter time that you have to do it about 2 hours beforehand because that is when the curb grabbing begins during that time of year. MK is the only park that risks closure to new entries due to capacity crowds and it usually does not happen during Easter but it has on occassion on Easter Sunday and sometimes other days. Highest risk of having it occur is when Easter falls during last two weeks of March or first few days of April. That seems to be the biggest "double whammy" crowd time since you get crowds as a result of the majority of schools having their break always the week before or of Easter but then there are also a huge minority of schools that always have it between mid-March and early April regardless of when Easter falls.
Epcot: Beginning by 10 most things are packed (Spaceship is packed earlier than that simply because it is the first thing everyone sees and head for when they enter). Beginning about 3 many things are easy to get on, e.g., Spaceship will have become a walk-on. However, Soarin' and Test Track can get up to 3 hour stand-by lines by 11 and stay that way into the evening. Make sure you check on shows at the stage near the American pavilion in Parade of Nations because they often have very good ones during Easter time. The walkway around the nations gets very crowded in the late afternoon to evening and thus plan to take longer to get to places if you have a reservation. Though there are no "light" crowd days during Easter, Epcot's somewhat lighter-than-huge days are Easter and the day before.
Studios: Crowds turn to huge by 10 or 10:30. It will usually be open to 10 or 11 although when they initially publish hours they may say only 8. Almost everything is hugely crowded from about 10 to 3. Tower and Rock n Rollercoaster can get sustained 90 minute or more lines with some relief during the afternoon parade and significant relief during Fantasmic when there is an early Fantasmic. Also, in late afternoon Tower can be as low as 30 minutes. Toy Story is a mess all day after first thing in the morning with 90 minute or longer lines forever. Moreover, the crowd is always gathered outside of it on the street and it gets so large that sometimes it is almost impossible to even walk through it to get from one side to other. Mermaid also has huge lines in late morning to late afternoon and then becomes somewhat easier to get on. Other than the ones mentioned, things can be fairly easy to get on after 3. When they have two Fantasmics in an evening, for the first one you need to show up at least 45 minutes early to assure a chance of getting in; the late one can then be a walk-on even at 5 minutes before show time. When only one Fantasmic at night, obey the at least 45 minute rule. Best way to assure a seat is the Fantasmic dinner package but call many months in advance. Easter is usually its somewhat light day.
AK: when they intially publish hours they may have AK closing at 5 or 6 and that will likely change to 8 as it has done for several years. As with others early morning is good but by 9:30 you have huge crowds. AK does not have wide walkways and thus walking around can be a problem because crowds get so thick. Also, plan to be wherever you want to be for the hour before and through the parade because once the crowds start for that you cannot even get from one place to another if it requires going through the area where the parade runs. Everest can get 2 1/2 hour sustained lines for most of the day. Others can be 90 minutes or more from mid morning to about 3 when they begin to taper off and by 4:30 or so, the lines can be quite short. For Lion King and Nemo stage shows you should show up well in advance (40 minutes or more to assure getting in). As with Epcot, its somewhat lighter days tend to be Easter and day before.
Pools/Waterparks: Resort pools can fill and it can be hard to find anywhere to sit except directly in the sun unless you arrive early. You also face the problem of those who claim tables with their stuff in the morning and then disappear for four hours. Noon to 3 are the most difficult hours for crowds. Waterparks, when weather is warm enough (usually but not always during that time), can fill to capacity by 11 and then open up again about 2. If you want to find a table in the shade you must arrive early.
Weather: usually some of the best weather of the year with warm days, mid-80s and pleasant evenings. Nevertheless there can sometimes be the cool day (60s).Thunderstorms occur but very often when they do they occur during the night while you are sleeping rather than during the day.
Decorations: Disney does not do Easter like Christmas. There will be some decorations but most hardly noticeable. A number of the resorts usually have egg-hunts and craft things on Easter and the bunny may show up. MK often has MR and Mrs. Bunny for character meets for week before and on Easter.
