We went there last year and it was pretty crowded. I would plan to get there before opening so you can get some of the popular rides out of the way before the hoards arrive. We ended up leaving around 3 o'clock last year because we couldn't handle the crowds.
I do have to say that I still enjoyed my Father's Day with my family at DL. We ate at Breakfast in the Park with Minnie and were able to enjoy the characters and the food.