I don't consider Github's issue tracker to be particularly good.
Sure its convenient if you just have a small project and don't want to host an issue tracker yourself and don't care about the usability of the issue tracker.
The "killer feature" of the issue tracker is that you don't need to create yet another login just to report a bug. Chances are you've reported an issue on github before, or if not you just have to create a user once, that you can use to report bugs on any github project.
I consider Github's issue tracker to be a significant step backward/in the wrong direction from Bugzilla for several reasons:
* defaults to markdown instead of plain text [1]
* no easy way to attach binary files[2]
* no easy way to attach files[3]
At least from a project developer's perspective I find bugzilla much easier to use (once you get used to it), and has more features.
There are some minor improvements in Github's issue tracker, but none that would want to make me switch.
[1] Whenever I paste some error message / shell output I need to escape it in
or blocks, otherwise it messes up the formatting. I initially created a lot of broken bugreports, that I had to edit once I've seen how bad it looked, of course then I found out you can preview the bug before submitting. IMHO text should be the default for bugreports, not markdown![2] they come in handy depending on the project. If the project deals with binary files, it is expected that bugreports may have to contain them as well
[3] Besides creating a gist and pointing to the gist you pretty much have to self-host any file you want to "attach" to a Github issue, unless I'm missing something.