Easter is April 16 next year. The two Easter weeks are typically the second and third most crowded weeks of the year behind Christmas. The most crowded time is when Easter is in late March or early April since you get a double whammy because, besides that there are many schools that traditonally have the week before or of Easter as their break, there is also a very large contingent that always has late March or beginning of April as the set break time. When Easter is late March or early April, you can get a real risk of park closures at MK due to overcrowding.
The problem with next year is that there are events other than Easter that could add to the already large crowd. That Star Wars convention mentioned above is one. The other is that Disney has scheduled the Star Wars Dark Side weekend with a half marathon for April 21-23 and that could result in larger crowds Easter week. Also just because Easter is late, does not mean the crowd size is going to be less than summer time as mentioned above. I have been both times and Easter, no matter when it occurs, always has crowds larger than any time in summer.
As you will see from comments of others, crowd size is at least partly a matter of personal perception and tolerance. Some will say the crowds are heavy but manageable, others that they are impossible. Having been Easter time a dozen times and also having been almost every other time of the year, I can give you some comparisons. You say you have mostly gone in May. To me May crowds are heavy but manageable. As far as crowd size goes, you should expect the Easter crowd to be about three times the size of crowds that you have seen in May. A noticeable difference will be street crowds, particularly at MK which can get so thick that it can take 40 minutes or more just to walk from one side of the park to the other (in May, you can do that trip in 15 to 20 minutes). Enter MK about 11:30 and get to the bottom of Main Street and look toward the castle and what you will see is not a street, not a sidewalk, but instead a mass of bobbing heads all right next to each other.
Fastpass is critical and you should not go expeecting to do a huge number of things without fastpasses. If you go at park opening, you have some chance to do a couple things without fastpasses before the corwds become huge. The standby lines for popular rides get very long by 11 and stay long through evening. Soarin and Test Track can get to 3 hours. Spalsh Mountain and the roller coasters at MK, and Toy Story and Rockin Rollercoaster at Studios, can get to 2 1/2 hours. Even something as innocuous as Swiss Family Treehouse can get to an hour. A time of day when lines may reduce to 30 minutes or less for some rides is during a parade and thus you might attempt something while the parade is going on. Since parks remain open late, such as MK to midnight or even 1, you can also sometimes find shorter lines during the last hour the park is open. Ideal parade watching spots, including curbside, start to fill 90 minutes to two hours before the parade begins. Be aware that morning times can be tricky since magic hours can disappear simply because they may open the parks to everyone early.
You should make any dinner reservations in park restaurants as far out as you can. True story: we were once at Cyrstal Palace on the Thursday before Easter at about 6 in the evening with a reservation and the people in line in front of us asked "Is there any dinner time available that we can get?" The CM looked at the computer for quite a while, saying nothing, and finally gave the answer: "I can give you next Tuesday at 8:30." In other words, without reservations made well in advance don't expect to eat at any popular buffet or table service restaurants. Moreover at key times for lunch between about 11 and 2:30, the lines at the counter service restaurants can get to 40 minutes or more and seating can be very difficult.
As to great Easter events, there really are not any. Disney treats Easter far more subdued than Christmas. You get some decorations and some addition to the parade, and the resorts on Easter Sunday typically have a type of Easter egg hunt, some crafts, and a visit from the bunny, and sometimes a Mr. and Mrs. bunny. Some of the restaurants at the resorts have an Easter brunch. Otherwise, what you mostly get is higher prices on food and drink. Note, that Easter Sunday is an extremely crowded day at MK mainly because many go there believing something special happens on Easter Sunday that you cannot see other days of the week. That is untrue and it is not worth the hassle going there on Easter Sunday, but also be aware that the day after Easter is often as bad at MK as Easter and there are no light days during the two weeks. Epcot and Animal Kingdom often have their lightest park days on Saturday and Easter Sunday, although "light" is a misnomer because it just means the very large crowds will not be quite as large those days.
Weather is usually ideal. You get some thunderstorms but very often at that time of year those happen overnight rather than during the day. One thing that keeps the parks staying a little short of being as bad as they are at Christmas is that waterparks are open during Easter and weather makes them usable, thus taking away some of the crowds that would otherwise be going to the parks. However, the waterparks can fill to capacity by 11 or 11:30), although they will usually open up again a few hours later.