We already collect some performance metrics that are useful. See here https://docs.appdynamics.com/display/PRO41/Monitor+IIS
As Akumar mentioned combine the metrics we collect with Health Rules and you will be alerted on key events.
You may be ineterested in collecting other counters we do not monitor out of the box. This extension http://www.appdynamics.com/community/exchange/extension/windows-performance-counter-configuration-extension/ is very helpful and you can quickly create a new configuration file for the agent.