OEM helps monitor across heterogenous systems which is key for big companies with various prod environments.

The automated alerts and notifications are key. Helps tide us admin through former sleepless nights. informs us proactively.

The new UI feature of 13c makes admin from tablets possible.

The number of plugins available makes this tool quite valuable for enterprise.

I have installed these EM versions from 11g, 12c, and 13c. So far Oracle support is quite helpful in the process.