As far as special decorations or events, there is not much as Disney does not treat Easter like it does Christmas. You will see some additional Easter decorations but most hardly noticeable; the daily MK parade gets some extra Easter themed floats for the week leading up to and including Easter Sunday: an Easter rabbit character sometimes appears (often just the White Rabbit in Easter garb), a few of the resort buffet restaurants have an Easter brunch, and a number of the resorts have Easter Egg hunts on Easter where the Easter Bunny and sometimes Mrs. Bunny show up. That is about it. Most restaurants simply continue with their regular daily menu. Park hours are usually long, like MK to 11 or 12 and MGM to 10:30 or 11.
As to crowds, if you went in December and November with light crowds (and thus obviously did not go Christmas Week), then mainly be glad that you were able to do everything then. Whatever crowd you saw multiply by about 4. MK mid-day gets to almost elbow to elbow on the streets and popular rides have 90 minute to 2 hour lines all day, all evening, with little or no let up; Test Track at Epcot and the Safari ride at AK can get to 3 hour lines; fastpasses tend to run out before noon for popular rides. PS's for dinner are necessary for any sit down restaurant. MK is usually packed to capacity on Easter Sunday. Many go with belief that something special happens there on Easter Sunday that does not occur the other days of week -- it doesn't so avoid MK that day if you can. Moreover, MK can reach capacity not only Easter Sunday but possibly a couple of other days (such as Saturday and Monday) so that off-site guests might not be able to get in during the afternoon-- thus get there in morning if going. Recommend arriving early in parks to hit some things before huge lines build (which usually occurs by 10), 11 to 3 in any park is most crowded time, from 4 to 8 many of the second tier rides (like Pirates and Haunted Mansion) are sometimes easy to get onto even though they might have hour or longer lines at 10 a.m. Moreover, you can find sometimes that lines reduce briefly to 30 minutes or less for the most popular rides during a parade or during the first Fantasmic at MGM (they often have two a night then). There are no e-nights during the Easter weeks. Epcot and MGM tend to have thier lighter days on day before and of Easter -- note though that lighter is relative as it is in comparison to the other hugely crowded days.
