Could be great
I deal with this stuff every day and while I'm not quite in the "hot garbage" camp, Atlassian software is like "there's some good stuff screaming to be let out".
The problem seems to be that it all should be torn down and rewritten, instead they just add yet more layers of enterprisy Java/Tomcat/Catalina.
Their QA is absolutely atrocious, I've had to deal with two showstopping regression bugs between *minor* version upgrades just in the last 2 weeks. Rollback without also rolling back the home directory and database is largely a lie (the supposed ability to do so is documented as "should work, no worries").
Functionality that used to be or should be built-in is increasingly outsourced to the marketplace - where you pay extra to third party vendors or Atlassian.
In 2018 you still can't execute fully unattended automated installation ab initio. The convolutions I - and others on the Atlassian forums - have had to do to get around this (especially for cloud deployments of the server products) are just frightening. Sometimes I look at my Cloudformation templates and weep.
Bugs and badly design configuration makes encryption-in-transit and at-rest a nightmare to set up. Another "forget about automating this".
OK, so maybe it *is* hot garbage.
Can't put my finger quite on it, but the downward trend seemed to really start - and accelerate - when they went public.
There is one exception: I love Bamboo! It kicks Jenkins' balls, it kicks CodeBuilt/Deploy/Pipeline to the curb. I've evaluated the lot like 3 times in the last year (there's a lot of pressure to go Jenkins) and every time I've come up with "out of my cold dead fingers".