it's worth a trip to Epcot when you are there as that is when they have their flower and garden festival and it is quite a spectacle. It's not as you would imagine simple beds of flowers but they model all sorts of Disney figures using flowers, trees, hedges and fruits (!) and they also turn all the fountains on full blast (which is great as often lately they have been shutting down water features to conserve water).
They also put on quite spectacular acrobatic and juggling displays that tour the park (last year they had a group doing stunts standing on huge stilts).
As Dave says, May is one of the best times of the year to go with regard to weather and crowds. Last year however was a bit of an anomaly as the heat was tremendous, hitting mid to high 90s most days whereas you would normally expect high 80s at that time of year - take your sun block!
We did find last year that IOS/Universal was particularly quiet with virtually no waiting time - we strolled straight into most rides. Disney was still busy - particularly Magic Kingdom, but then I think that is always the case.
Try to go to Downtown Disney if you can fit it into your schedule. It can be found within the Disney Complex but you don't need your tickets to get into it and there are lots of things to do there and some good places to eat.
Have a wonderful time (I am envious as we cancelled our trip this month to do an extension instead
Jackie