Pros
ADP is a very stable company, that provides excellent job security for it's employees. They have good benefits, and the raises/bonuses are regular and predictable. They are also very reluctant to terminate, and will take every measure to attempt to avoid firing an employee. ADP is a good place to work if you need a stable job, that doesn't interfere with the rest of your life.
Kontras
ADP is not a company filled with bright minds and overachievers. It is an "old school", conservative corporation in which people are underpaid, and are often promoted not on merit, but simply because they have been employed for X number of years. They are slow to promote, which makes it difficult to find challenge and new learning opportunities. They put more stock in "years on the job" than they do in ability. I can personally attest to this, as an employee who received glowing reviews for four years straight, but was always told that advancement would "take more time".