Pros
The benefits are incredible. With a family of four, all healthcare benefits are paid. Atlassian works hard to make sure the employees are taken care of and it shows. They invest in programs to support the mental health of everyone and provide ways to connect with others virtually (through the Pandemic). The leaders are open to feedback and are transparent, answering the tough questions in company-wide meetings, even when it's hard. The culture has been painstakingly cultivated to include all kinds of people. As a parent of a trans child, this in particular has been inspiring to see. There is an emphasis on promotion from within, and there are opportunities to grow your skills to serve the company in new ways.
Cons
As an organization that has grown through acquisition, not all systems are integrated, which can make for a difficult experience in learning how to do your day-to-day job. Atlassian is a largely self-organized, self-driven set of software nerds (I count myself among them and don't say that as an insult), as such, it can be difficult to find a human to help you to find answers. It's written down somewhere on a Confluence page, but everything is in Confluence, and if you lack the history and navigational expertise in that platform, it can be very hard to find what you need. Support is always a ticket, but I'm never sure what kind of ticket, what help desk, etc. Be prepared to have lots of systems to learn.