Some screenshots can illustrate what i mean:

How long would it take to create such a query in foobar and how many people would it understand? Beside of that it wouldn't be possible to translate all parts of it.
Jriver's query wizard stands out due to its convenience: whenever you use the "is" operator for a field you get offered the opportunity to check any number of all possible values that exist in your library - also it handles tags with multiple values very well as it offers for such tags "is all", "is any", "not is any" as operators. Look here:

Another great feature: After each added rule the lists are sorted and all the entries that matches the rules before are displayed first:

I would love to see that somedays in foobar 2000. Naturally such a feature requires that foobar is able to distinguish between different type of tags as therefrom it depends which operators have to be offered. Foobar actually can recognize the most type of fields:
1. Multiline line fields are defined in the advanced preferences
2. Multivalue fields are also defined there
3. Fields with a limited amount of values are defined in quick tagger preferences
4. Date fields are not typed in by users but provided by components
There are several typical areas of foobar where such a query editor would make a good job:
1. In all the filter toolbars (album list, facets, ...)
2. As simple and standalone playlist generator (callable in main menu -> Library f.e)
3. For creation of storeable subsets of library (the only components i know which allow storing of subsets are Playlist Generator for foobar2000 0.8 and Playlist Tree)
and so on...
Hope for some comments!
