It's not fundamentally different for many WDW guests (specifically non-locals who only visit one park per day, plan well in advance, and don't change that plan), but that doesn't mean it's not different for many others.
For those "spontaneous" types who prefer not to plan ahead, or those who need to change their plan last minute, the Park Pass system is less flexible. Previously, park capacity was essentially one big bucket, so with the exception of the top 3 or 4 busiest days of the year, guests could easily decide to go to a different park day-of. However, with the new system, capacity is now divided between three pools (APs, on-property resort guests, and everyone else), so a park could still have availability, but you might not be able to make a day-of reservation because there are no more available reservations in your particular pool. Also, a big difference between then and now for the non-planners is that you didn't have to make FP+ reservations to get into a park, so for a few people I know who didn't even bother with FP+, and were used to just showing up to a park, not being able to even get into a park without a reservation feels restrictive to them.
People with park hoppers could previously reserve afternoon FP+ for one park, but then rope drop a different park in the morning, and then head to their "reserved" park to use their FPs, which made it possible to tour parks more efficiently. With Park Pass reservations, you have to go to your reserved park first, and can't hop until 2PM. So if FP returns while the Park Pass requirements are still in place, this strategy would likely not be possible.
Annual passholders are probably most affected by the new reservation system. They can only reserve 3 days at a time, so local APs can't visit any time they want and just pop into a park on a whim like they could before. They now might need to plan their visits in advance, and they can't visit any parks while they have 3 outstanding reservations; so if, for example, they have guests coming into town, and to be safe, they reserve their 3 days months in advance, until the date of their reservations, they wouldn't be able to visit the parks at all. Out of state APs are potentially very much affected by the Park Pass system as well. While APs can reserve park days for their entire trip in advance if they are staying at an on-property resort, unfortunately, APs who are staying off-property can only reserve the first 3 days of their trip in advance, and then have to reserve the rest of their parks day-to-day during their trip at which time availability might possibly be gone. So for those people, the Park Pass reservation system is a significant change from how they were able to schedule their trips before.