"As a senior project manager, I have tracked a lot of metrics over the years. However, there are several key items I feel every agile project team should keep track of. First, it is critical for a team to know its velocity. Knowing your velocity from sprint-to-sprint helps you to identify issues and project future performance. It is also a key input to the estimation process. Likewise, it is important to track a team's cost per point, or cost per feature, or something similar. This helps with estimation and tells the story of a team's performance improvement or decline as well.
I also feel it is critical to track the remaining minimally viable product stories complete vs. left to complete. This gives a sense of how close a project team is to developing a minimally viable product that can be released and tested while the remaining features are built. Feedback is critical to the agile process, and this number helps a team estimate when that important feedback loop will be in place.
Finally, I track average time to resolve for defects and support issues. Defects often represent unexpected work, and it is important to get a sense of the volume of this work over time for planning and process improvement purposes."