BitBucket is a follower, not a leader, and has managed to get a lot of what makes Github work well added - inline comments are great.
BitBucket has lead in one area though - much like a 'merge pull request', on each change there's an Approve button.
If you are happy with a commit, it's a click away - you don't even have to say 'LGTM', if not, have a discussion.
There are two problems with this though:
- Every time you hit the button, notifications are sent
- The review is per commit, not per feature or branch. If you use a simple 'all in' model, it's hard to group a stream of work - later fixes are applied that invalidate your review, all in the same push.
The best answer I have for issue 1 is to create email rules. If it has to works "commit approved" from bitbucket.org, mark as read and archive it.
This dramatically changes the signal to noise ratio, but lets you still leverage the visual indications of review having taken place.
For the second, feature branches and pull requests are the next best bet - BitBucket allows you to do a pull request from a feature branch on your repository to master.
This lets review take place on sets of code and features; and works extremely well for integrating stable changes only.