It is very easy to use and customization makes it very powerful. I have submitted more than one "idea" to the developers that has been implemented, i.e. they are very eager to continuously make the product better. It was extremely easy to integrate into our github installation and our Continuous Integration environment.
Within as scrum framework seem tailored to that environment and it works well also being a saas product made it easy to deploy. The support that came with rally was really quite good. The team from rally were happy to help with their product and the process surrounding it. The hierarchy and project model allowed for the all the work and relationships in the organisation to be modelled in one place.
At the time (2016) the product was a little inflexible, if you were not doing a scrum like a process it was hard to fit with the tool and often resulted in people working out of excel. Also did not have straightforward integration with other wiki tools etc. Also needed the ability to directly discuss and send emails from within the tool. Note this was the state pre CA taking over.
Fairly cheap, and does do a lot of basic functionality that any team just starting the agile process may need to understand. Does have good visibility from top to bottom
It is the opposite of feature-rich. Most teams running enterprise agile on a large scale will likely struggle with its' massive lack of features many people come to expect from these tools.