I'm probably in the minority but I have more satisfying visits during peak seasons, even though they are more crowded. I enjoy the longer operating hours and the perks that come with them.
For instance, when the MK is open from 8 AM - MIDNIGHT during a peak period, they will run the night parade (currently MSEP) twice a night EVERY night of the week instead of once a night just a few nights a week during the highly touted "slow season".
So you can walk up to the never-crowded 11 PM parade in Frontierland right as the parade is getting there, have a perfect front row spot to yourself, and interact with the various characters in the parade (because there aren't throngs of other people wall-to-wall in the streets competing for their attention).
Then, when the 11 PM parade is over, on nights when the MK closes at midnight or 1 AM, even the most popular attractions in the park will usually be a walk-on!
Compare this to the highly touted "slow season" such as in January with an 8 PM close and the parade once a night, just a few nights a week, at 7PM.
You basically have to stop doing attractions at some time during the 6 PM hour to get a good spot, and then the parade itself is EXTREMELY crowded because everyone at the resort there that week is basically ALL in the MK at that moment trying to see the parade (since it is only presented 2 or 3 times a week during slow season as opposed to 14
during peak season).
And then, after the parade, you can't really do to many attractions or else risk missing the beginning of the fireworks starting at 8 PM - park closing.
Whenever the MK closes WITH the fireworks show, no matter how "slow" the season, leaving the park is an absolute ZOO with the transportation system overstrained.
Also, when the MK opens at 8 AM each day in "peak season", it is typically less crowded that first hour than a 9 AM first hour is during slow season. This is because there are far fewer people willing to get up that early, no matter how many people are at WDW at that time. So, you have more time in the morning during "peak season" to "surf the wave of walk-ons" before the late sleepers start filling up the park, than you do during slow season.
Sure, the peak middle of the day is admitedly MUCH more crowded during peak season than slow season, but if you know how to exploit, er, manipulate, er, utilize the Fastpass system to your maximum advantage (which is free and available to ALL guests), you can easily spend an entire day in the MK during peak times and never have to wait more than 15-20 minutes for anything! (a lot of non-FP attractions, like the Peoplemover, Railroad, Riverboat, Carousel Of Progress, Tiki Room, Country Bears, etc, can be walk-ons on even the most crowded of days)
I know I get to experience more attractions per day at the MK on a peak 8 AM - 12 AM day than I can on a "slow" 9 AM - 8 PM day. I simply run out of time on the short day, whereas FP cancels out any insanely long waits that would bog down the long peak days.
The same principle I discussed above for MSEP/Spectro also works the same way for Fantasmic! at the Studios.
Think of the hassle seeing Fantasmic! can be now that they have reduced the number of shows per week during the "slow" seasons.
Like in January it may just be performed 2 nights a week, 1 show a night. So naturally, EVERYONE in WDW that week is going to be in the Studios that night, trying to see that show. With the skimpy closing time/show time of 7 PM, you will have to stop doing attractions at 6 PM just to make sure you get in the show.
Compare that to a peak season close at 10 PM with Fantasmic! presented at 9 PM and then again at 10:30 PM twice a night, EVERY NIGHT, or 14
times a week!
You can go to the Studios ANY day of the week and see the show, without having to pick the one or two nights a week it is presented.
And while most people in the park are queueing up for that first 9 PM show an hour before it starts, losing attraction time, you have the attractions virtually to yourself all the way up until the attractions close at 10! And then you can casually walk into that second show right before it starts and get a GREAT seat!
For all of the above reasons, I'll take peak seasons anyday!
(just an alternate viewpoint, written from the point of view of having lots of WDW experience as a seasonal local the past 5 years)