We did a week in May from the 13-20th.
We had one day where it rained lightly in the morning and one day where it was warmer than we'd have liked. Otherwise the weather was gorgeous!
There were a LOT of marginally supervised middle schoolers in the parks on end of the year band/class trips. Not a major crisis, but probably the one real irritation of the trip. More time than I might like was spent reminding other people's children to wait their turns, but again, it wasn't "ruin your trip" bad.
Lines were pretty reasonable in general. We make good use of fast passes and the wait times board (and baby swap!), so we only had two waits over 20 minutes. DS managed 6 rides in a row on BTMRR at one point. Oh- we did use a chunk of our MM to get in line for PFF before it opened so we were like third in line.