I use it every day, and I think it's great (including the UI). I'm curious to see what, specifically, you find terrible about it, and which bug tracking system you find to be better.
I think the main reason people bash the UI is because it doesn't look shiny. I think the reason people don't like the rest of it is because it forces you to use it a certain way and people don't spend the time to actually learn or get used to it. It's not perfect (speed wise), but if you give into how it wants you to use it, it works well.
