It should have a proper bidirectional email interface. I guess you were more thinking about the view of a developer of the product or project, but what I hate

It should have a proper bidirectional email interface. I guess you were more thinking about the view of a developer of the product or project, but what I hate with a passion is when other people expect that I create an account on their issue tracker and then use their user interface for what for all intents and purposes is writing them an email. Even more fun when that includes the need to enter into a contract with a third party (like GitHub) and you would have to read pages and pages of legalese first. If you want to have some UI for managing bug metadata, great, I don't mind, but don't expect me to use your UI. A bug tracker in some regards is a sort of specialized electronic messaging program. If you use Thunderbird, you don't ask me to "create an account with Thunderbird" or to install Thunderbird, you simply hand me your email address, and I use my MUA to send you an email--which you can read and archive and whatever in whatever MUA you prefer. It makes no sense to handle issue trackers fundamentally differently. But the same at least to a degree also applies for the developer side of things. While some of the issue tracker functionality probably is not a good fit for email, a lot of the day to day stuff very much is, and that even includes some of the management of metadata, so a good issue tracker should also have at the very least a bidirectional email interface, optimally with the possibility to manipulate bug meta data via email as well--see the Debian bug tracker for an example of a very powerful email issue tracker interface. An issue is essentially a thread, and as such, it should be mapped to an email thread, where you can reply to previous messages just as you can to any other email, without the need to switch to a different user interface.