The interserver website is easy for my clients who are older than I am, so they can easily navigate it themselves! It's also very user friendly - no matter how complex your needs may be, you will not find an interface that doesn't make sense or work well once you figure out what buttons do what.
There really isn't anything wrong about this system; if we need more features added in future releases (as our business grows), there should definitely be room for expansion without making changes to something else within the platform. We use IS as part of our payroll service. Our client base consists primarily of small companies/businesses between 10-50 employees each year.