We have gone several times over/before/after the Easter period and the WDW resorts fill up the weekend before the Easter weekend and from then on the parks and resorts remain busy until after Easter. As Hilary says, with an early Easter break, you have Spring Break too so the parks remained busy for a time after Easter. However, next year, hopefully after the weekend, there should be a marked decrease in numbers.
April is glorious - zero humidity, plenty of lovely sunshine!
One year, we wanted to see the Easter parade and we braved a MOBBED MK, to watch the parade - this was being filmed the weekend before Easter on the Saturday. The parade itself was wonderful but often interrupted for the filming and so took ages and ages to finish!! ( we were notified of this before we entered the park) As soon as the parade was over we hopped to EPCOT. However, we've given the parks a wide berth since then on or near Easter.