We actually just got back today from a week at the Universal parks and it was very crowded in my opinion. To be fair I have only gone in September in the past so the crowds were huge compared to then. The first 4 days we didn't have express because we stayed at Bonnet Creek but our last 3 days we stayed onsite and had the express pass and here is what I noticed.
When we didn't have the pass we got there at park opening and walked on Spiderman, Hulk, Storm Force, Jurassic Park, Pluto's Barge and Ripsaw falls only had a five minute wait but we wanted to wait until later in the day to do it but when we went back it was a 60 min wait. FJ was posted a 45 min wait but we were on and off in only 20 min. The next day over at the Studios DP had a 10 wait at opening, we walked on ET, MIB had a 5 min wait, Mummy had a 10 min wait, Simpsons was a walk on and Rip Rocket had a 10 min wait. I found that if you got there at opening you could ride most without much of a wait but by 11 or so the lines were super long with about a 60 to 90 min wait. So without the express we usually left by noon when the lines were too long but with the express we were able to stay the entire day and enjoy the rides multiple times. However, on some rides even with the express pass later in the day you still had a little wait, for example DM was still 30 min for express but standby was 90 so it still beat waiting in the standby line. I don't know if next time we would give up the space we had at Bonnet creek for the express pass. We still got to ride everything we wanted at least once as long as we got there when the park opened.