We were there last year on Memorial Day!

I agree that it was HOT! We consumed gallons of water to stay hydrated and cool (and learned where all the bathrooms are...

).
It was crowded - the paths and such are narrow, so we sometimes ran into a bottleneck in the crowd (especially around the big attractions). We used FP as much as possible, but they went quickly. On the other hand, it wasn't unbearable, and we did manage to get into a couple attractions without FP in less than 30 minutes. We enjoyed wandering "off the beaten track" and finding the tucked out of the way stuff as much as possible. We also ate at "weird" times - did lunch at 2:30, for example - so we could use the lunch hour to see things while other people were eating, and the restaurant was less crowded when we got our food.
I did hear that AK was not nearly as crowded on Memorial Day as the other 3 parks, so I was glad we picked that one for that day!