It is an awesome tool to use with great ROI, we have been using this tool extensively in most of our projects to reduce the manual regression efforts and to prevent production defects. Another beauty of this tool is to extend and integrate with other functional & non functional tools(Jmeter, OWASP ZAP, Appium ..etc.)
Recently we have implemented the Extended Reporting to support rich reporting structure with Charts,Dashboards that would be easy for stakeholders to Analyze and arrive at decisions.
Compatibility issues with newer versions of browsers (IE & Firefox) and latest server versions, but this can be addressed with some workarounds.
Handling Windows based dialogs (or) performaning Non browser action can bit challenging, so far we are using AutoIT tool to perform this.
Rather QTP or any other Commercial tools, Selenium expects more Techinical(Prograaming) expertise, but other end this feature makes selenium more flexible
We had compatibility issues with some newer versions of browsers.
We've had no issues with stability.
We've had no issues with scalability.