One idea is to group the child category filters below the parent category. This makes it clear that the child category filters will return a subset of the parent:
download bmml source – Wireframes created with Balsamiq Mockups
This design gives you flexibility in the event that your taxonomy changes. For example if a new subject type is created for Product Reviews but not videos, you could add that in without having to make any changes to the control's logic.
The more I have thought about it, the more I dislike having "All" as an option in the UI at all.
Marcos' question about faceted search made a good point:
...most of the websites use a set of check boxes, and the All function is done by checking all the boxes, eg. Kayak or Amazon do it like this.
With only 3 review types, it is fairly simple for a user to select 1, 2, or 3 options. As a result I'd instead use the following UI:
download bmml source
Update 2 Incorporated kountor's excellent suggestion of pre-checking child categories.