Unfortunately it all comes down to the particular office you work in and your direct manager. If you have a bad manager, you are stuck. Upper management and HR will accept your complaints, but nothing will be done. After I was there for a while a bad manager came in and his entire team quit within a year. He had 100% turnover in one year. All of the reps complained to upper management but nothing changed.
You will see mixed reviews - Paychex Great and Paychex Horrible - it's all about the District Manager and Zone Manager .
Please note that there are different divisions: CORE payroll, MMS Payroll, HR Premier and 401K/FSA - each divisions has it's own District Manager that you report to.
Best advice is to listen to your instincts when you interview. See if it feels like a bad office or manager - or if it's good.
Keep in mind management staff can change. A previously bad office can become a great office when there is different management.