It works just fine for me (though my repos are small), however it is extremely slow when ssh'ing through Tramp onto a Linux host. I still put up with it because the interface is so good.
The real problem is that the web is now too complex to the point that it's impossible to safely implement it. And W3C keeps trying to add new features to it. At some point we have to stop and consider whether all this cruft is even necessary.
I prefer JIRA. I used Github issues and my current place of work uses Redmine, and neither of them are as nice to use. I like the ability to customize your dashboard to show the exact issues you're interested in, and that you can filter them by basically everything.