I went last year about the same time in May. Crowds were almost non-existant and the most I waited for a line was about 45 minutes and those were for the big ticket rides. My tip, if a line is longer than 1 hour, either get a fastpass or come back to that ride later.
Also, the weather was wonderful. Warm, but not stiffling. Just keep a bottle of water with you at all times and you'll be fine.
I wish I were going back in May, but unfortuately I cannot. It was absolutely wonderful.