Everything. 
- This could be a good start: “Seeking Guidance on Implementing Windows Server Monitoring with Grafana OSS”
- Good community support. (Lack of answers to the fairly simple question above may be an indicator that OTel / Grafana may be too heavy of a lift for your average sysadmin.)
- Big 4 (CPU, memory, storage, network).
- Ability to “walk” processes and services, and add them to monitoring templates on the fly.
- Disk and processor queue lengths, capacity and resource exhaustion charts.
- Custom PS scripts for monitoring file and directory sizes and counters.
- Intelligent alerting with reusable macros and conditions. (E.g. set up Slack channel targets in one place, not in every Slack alert; set up firing conditions in each alert allowing arbitrary muting depending on the source of the alert and other variables.)