I used this addon already for yeasr with XF 1.5x. This addon is a life-saver for busy forums and busy moderators. For version XF 1.5x this is 5 stars.
The only thing which is missing now with this new version for XF2.1x is that you do not get the content of the report anymore within that emaill. Therefore this time only 4 stars.
In the version for XF 1.5x this was still delivered with the text the users wrote in his report, so you could decide whether it is necessary to act immediately (i.e. spam) or whether you can do it also later on.
As soon as this is also implemented in this new version for XF2.x, I will rate it again 5 stars.
sonnb - Report Alert 2.0.0 RC
Send Alerts and Emails to Moderators for various Report actions