Although they are both doing same thing, providing secure access to network, they both are doing it differently and of course they both have different features. NAC is much better in device profiling, providing guest access, monitoring, troubleshooting and many others....
Here is a comparison of NAC (formerly known as Clean Access) and ISE.
As far as i know NAC is now obsolete and several models are already end-of-life. ISE is now way to go when implementing network access control.
That was most likely Guest Portal and Central Web Authentication. Both of these features are supported on ISE. More details here: http://www.cisco.com/c/en/us/support/docs/security/identity-services-engine/115732-central-web-auth-00.html