Most of the configuration can be done by you - this is good and bad because you need to devote a good bit of time to learning all the ins and outs of the system, and it is indeed, time consuming. Also, if you need anything configured that was not covered in implementation, it will cost you, and it will take a good bit of time - such as benefit feeds or customized reports, or any re-configuring of your org.
As with every system I've used in the past 20+ years, leave accruals, (PTO, Sick, VAC, etc.), are confusing and complicated. Also, creating a custom report can be tricky.
Training costs are too high. Review collected by and hosted on G2.com.