We installed OpenNMS 18.0.1 on Windows Server 2012. Although the vendor warned that the Windows install was a bit tricky compared to Linux, we actually found the opposite to be true.
After the service was started we connected via web interface and began finding and monitoring network nodes. No errors, no problems. We found the management interface layout clean and logical. No client agents are needed to run basic monitoring tasks on discovered or manually-added nodes. OpenNMS is event-driven and events are displayed on an easy to read dashboard.
We liked the robust reporting feature using Jasper Reports.