The basic package seems to work OK. But bbPress is also not that well integrated with WordPress. For example search is not integrated.
But most of all Blog Posts and Forums/Topics are completely unrelated. So should a user follow up a blog post with a comment or a forum post? It is not clear. Ideally Forum names and Blog taxonomies should be united somehow. A forum should mainly just be a different view of a blog. But in bbpress they are completely different objects.
(They are physically stored in the Posts table, but that does not actually count for much except maybe export/import.)
And if they are not integrated, apart from maybe some theming, then why not just use a separate, specialist forum package? Common usernames is really all that you get.
bbPress also contains a vast amount of code that does permissions somewhat differently from the rest of WordPress.
Approximately, it tries to have two roles per user, a normal wordpress one and an independent bbpress one. The magic "Auto Role" option can set the latter for all new users. At the bottom of the Admin Users dialog there is an option to set the Forum Role.
There is something called "Dynamic Roles". You can end up with capabilites that were not on your roles somehow. And for multisite, you get capabilities to all sites if you get capabilities to any site.
It all feels confused, with no less than three files named capability.php in the distribution.