We were there Tuesday, Thursday, and Friday of this past week. Tuesday was raining so it was deserted. Thursday it was supposed to rain all day according to weather.com but didn't rain at all and there was 12,000 people in the park (almost no one) Friday it wasn't very busy either and completely cleared out with the rain.
Not sure if this week is an anomaly, but the crowds have seemed lighter this year compared to the past two years. I would go on Tuesday or Thursday of this week if I were you. Do not go on a weekend unless you are willing to shell out big bucks for a Flash Pass.