I find JIRA really usefull not only for issue tracking but as a task management tool fully adaptable to the user needs. Since its first versions, it has evolved with new features to cover the needs that have emerged in the agile project management. Today you can use JIRA to manage your agile projects based on Scrum, or Kanban methodologies as well as to track project tasks or support tickets.
The tools is completelly configurable, it allows to define custom issue types, fields, screens, workflows, notifications and configurations to support any scenario or issue type.
Additionally the Atlassian Marketplace offers more than 1.500 plugins that can be used to extend the product features.
Finally the tool can be integrated with several other tools used in the Software Development process such as Jenkins, Git, etc. and can be part of a DevOps toolset for your Company or customers.
JIRA flaws I find are some limitations regarding the nested sub-taks level allowed (only two). The tools allows to relate tasks but only some features are available only for sub-taks.
Another flaw is the way it stores custom fields in the database (in a unique colum for different types), makes dificult to optimize the database table implementing indexes to optimize the access. On the other hand, JIRA implements its own indexing system in order to keep the performance on the system.
On the other hand, I found really difficult to migrate versions due to the use of third-party plugins. JIRA doesn't have any validation tool for that and you have to checkit before migration because not allways the plugins will be supported in the new versions, so think twice before install any plugin in JIRA.
Pricing for me its another flawback, it has been increased disproportionately. I started using first versions of JIRA almost for free, we pay for the most complete license about 4k licensing and today you could pay up to 48k, more than 10 times the initial licensing prices. These guys are doing a good work but the should not abuse with pricing if the want to keep on doing good business.
A tool usefull not only for issue tracking but as a task management tool fully adaptable to the user, company and customer needs.
Supporting project management, implementing support / ticketing tool, integration with other tools involved in the Software Development process,