issues in network monitoring

I was part of a team that built an automated network monitoring tool for very large networks. The tool was built on FreeBSD, Perl, and Postgres and was fun to build. I have an urge to try and build an up to date version of this tool for the modern cloud. I was wondering what the state of network monitoring you use today for your startups and enterprises? What tools do you use? What problems do you face? What are absolute pain points / problems which you would like for your monitoring solution to solve? Thanks you for your help!