It would be interesting to separate out the complaints about the CONCEPT of FP +, the DETAILS of how it is being implemented ( number of FP available, tiering, ability to make FP+ reservations in more than one park,etc.)' and the SYSTEM for making reservations.
I suspect that people who don't like the concept are more likely to be unhappy with the system, whereas, people who are happy with the concept are more likely to be tolerant of the system.
Here is how I classify myself:
Concept: I am somewhere between indifferent and happy about the concept. We have never been big FP users; we get to a park early, take a break, and usually hop to another park. But, because we often have to visit at busy times because of family schedules, I think FP+ will allow us to do some more attractions at our second park of the day.
Details: A limit of 3 is fine with me and, although I would love unlimited availability, I can understand why tiering is necessary to give more people a shot at the biggest headliners. I would also like the option of choosing to make reservations in more than 1 park in a day. But, I also understand that the details will always be subject to change, so I'm not going to get too worked up about them.
System: The system for making reservations is not as efficient as I would like but, because I generally like the concept, I will deal with the inefficiencies and hope for them to be improved as the system develops.