Pros
Atlassian has recruited some really smart, hard-working people, and given then a lot of leeway, budget, and support to pursue their ideas. We're growing like crazy, and hiring so many new people, it's amazing. It's provided a lot of opportunity to expand responsibilities, attack new challenges and grow my career. As a woman, it's among the most friendly, open and supportive tech companies I've ever worked at - I haven't even had a whiff of the sexual harassment types of things I saw over the years. Maybe helps that there's not a sales team and the big ego testosterone department that usually comes with it. The management team is humble and philanthropic - it's genuinely inspiring to work with them and for them. It doesn't feel like everyone's just there for the money and there are very few politics relative to other companies I've worked at before. The average employee is also much more philanthropically/socially minded than average tech colleague I've had - feels like we're doing good work and doing good in the world at the same time.
Cons
It's a straight-shooter culture with a very open online wiki. Your work will often be a public debate and people won't necessarily hold the punches telling you what they think, even if they don't have all the information. With a little bit of self-assertiveness and resilience, you can make it through - in general people are kind and bright, and will be much more reasonable if you catch them in person. But sometimes they can get a little sharper when they're making online comments vs. what they would say in person. The management team also tells it like it is. Consistent with other engineering cultures I've worked in - everyone's more analytical and straight-shooting vs. the warm, fuzzy beat-around the bush side of the continuum.