Overall, the biggest con of Fastpass+ is it's efficiency during peak times, which will probably improve once Cast Members and guests become more used to the system. A huge con for those who are not relying on the Fastpass+ system seems to be longer wait times, since Fastpass+ guests are a huge priority. Expect to wait for an entire line of Fastpass+ guests to be let on a ride at a much faster and higher rate than the normal line guests, but that shouldn't be a surprise. The original Fastpass had that problem too on it's more popular rides. Now, there's just more rides on the system, and less Fastpasses are allowed. Fastpass lines should usually be shorter now, which I guess is a big pro for both people in the Fastpass and normal lines.
The part I bolded is my biggest problem with the new system.
Under the original system there were only 9 attractions on the system at the MK (and only about 6 or 7 of those were realistically needed on most days). A savvy parkgoer like myself who loves to "open" parks at rope drop and stay to close could easily make sure they were able to get one for each attraction on the system if they wanted, and still get repeats on faves. On a typical MK full day, it was not uncommon for me to use 10 or more FPs, usually using 3 or 4 for Space Mountain re-rides alone!
I NEVER rode a FP attraction under the old system without having a FP, unless it was early in the day or late at night and the ride was a walk-on.
This means the only queues I had a potential long wait in were those for attractions not on the system, but only a few of these ever reached more than 30 minutes in my experience unless you hit them in the midday "peak window" of a very busy day. Most attractions not on the system were usually short waits to walk-ons.
Under the new system, you have, as you said, fewer FPs allowed per person, but with MORE attractions on the system. This means that the savvy parkgoer who NEVER had to use standby under the old system for anything on the system will have to get used to longer standby waits for attractions they are used to using FP for; but ALSO the standby waits for rides they never used to need a FP for (such as Dumbo, Barnstormer, Small World, Pirates, Mansion, Speedway, etc), will now obviously be longer waits then they were before they were added to the system.
Even in a park like Epcot, where one typically only needed FPs for Soarin' and Test Track (and MAYBE Maelstrom and Mission Space, depending on the season and time of day you wanted to ride them), the new system still makes it imposible to utilize the system to the fullest potential of the old system, thanks to the "tier system" in which FPs for Soarin' and Test Track cannot be acquired in the same day.
So who benefits from the new system?
Well, looking at it objectively, any of the resortsters (ie, hotel guests) who liked to sleep late and then complained that the most popular FPs (ie, Soarin, Toy Story Midway Mania) were gone by the time they got to the park can now get theirs early without having to wake up early. And people who didn't do full days at the parks and/or utilize the old system to its fullest potential won't feel the hit of this new system as much as the hard core open-close parkies like me.
For those who DID utilize the original system to its fullest potential, by putting the time in waking up early and "pounding the pavement" doing a full park day, there is no denying that this "socialistic redistribution" of FP benefits by "leveling the playing field" will lead to more time waiting in queues, and fewer attractions experienced per day compared to the standards we have gotten used to in the original system.
I even think its possible that by putting so many attractions on the system (at least in the MK), it is possible that the hardcore open-close parkgoer will experience fewer MK attractions per day in this new system than they could in the days before ANY FP system existed (whereas with the original FP system, there was CLEARLY a significant spike in what you could experience per day, compared to pre-FP days).
All I can say is I am glad my WDW AP expired in 2012 and I don't have to deal with "Magic Bands" (TM) and "Fastpass Plus" (TM).
I'm too busy enjoying Universal and Islands of Adventure, where my Premier Annual Pass gives me a free walk-on "Express" entry to EACH attraction in BOTH parks EVERY DAY to be used whenever I choose. No worrying about times, "reservations", etc, or having to scurry around the park collecting FPs, or having to do it at a kiosk. I just scan my annual pass at each attraction entrance when I'm ready to ride it, and can then enter that attraction's Express Queue. With that AP I also get free PREFERRED parking and a 20 percent discount on food and merch.
I'm also enjoying the benefits of my Sea World/Busch Gardens Platinum Annual Pass, which include "stay seated" RE-RIDES on most major coasters and a few other attractions, reserved seats in all the major shows in the best section of the theatre, free PREFERRED parking, and food/merch discounts of 10 percent that sometimes go as high as 20 or even 30 during certain parts of the year.
In short, both those major Central Florida park operators treat their highest-level Annual Passholders like ROYALTY compared to the perks of a WDW Premium AP (which is even more noticable with the reduction in FP access at WDW).
PS. I am glad that at least Disneyland is still using the original FP system!