Hive mind: What do you look for in choosing a monitoring tool, particularly for #microservices development?

A colleague and I are working on a blog post that aims to give useful, non-obvious guidance. What should we be sure to include... and why do you include that?

Note that we aren't aiming to recommend or endorse any particular monitoring tool. This is purely an effort to help techies identify the criteria so they can make a good choice, based on expert opinion. With you being the expert.