It's a good very basic forums environment. As my website uses buddypress I have little choice about what forums software I can use so I am stuck with bbpress. The main problem I have with this plugin is that it relies heavily on plugins and unfortunately the plugins for bbpress are not great in number.
Basic things such as forums polls for users, post counts and ranks, preview buttons etc etc are not available and if anyone is very used to very well established forums software like vbulletin you will find bbpress severely lacking.
I hope they stop relying so much on the plugin environment in the future or at the very least the plugin environment picks up the slack and starts increasing in number for the much needed functions that are missing.
I will give it a 3/5 because it's on the right track just nowhere near perfect. And 3 is being generous.