Get exception messages from a custom SharePoint REST service

I am experiencing some difficulties in managing errors raised from a custom REST web service deployed to SharePoint ISAPI folder I developed.

My service is pretty simple. I deployed an .svc file to the ISAPI folder, and configured the service to use the MultipleBaseAddressWebServiceHostFactory factory (the custom service is REST based).

<%@ ServiceHost Language="C#" Debug="true"
Service="..."  
CodeBehind="....."
Factory="Microsoft.SharePoint.Client.Services.MultipleBaseAddressWebServiceHostFactory, 
   Microsoft.SharePoint.Client.ServerRuntime, Version=15.0.0.0, Culture=neutral, 
   PublicKeyToken=71e9bce111e9429c" %>

On the service I have a method configured as a WebInvoke operation:

[OperationContract]
[WebInvoke(Method = "POST", UriTemplate = "Foo?param1={param1}&param2={param2}&param3={param3}&param4={param4}")]
bool Foo(string param1, string param2, string param3, string param4)

My main issue is not begin able to correctly handle errors raised by the service (for sake of simplicity, let just assume the service method just throws a new ApplicationException, you will see why later).

If my service method throws an exception, the call seem to just return with status 200-OK, so jquery.ajax/angularjs $http think that the call has been successful and execute the promise success handler instead of the error one.

The only way I am able to actually have the error handler begin executed is if the exception I throw in my service inherits from SystemException: those exception seem to be handled in a different way and actually manage to trigger a 400 response. Still, in this case in my javascript error handler my error argument seem to be a string containing the SharePoint error page. I have confirmed by using the IE dev toolbar that in case of error, my service response body actually contains the full html source for the SharePoint error page.

I think I must be missing something obvious here. Can anyone provide help shedding some light on the issue? I would like to be able to receive just an error message from my service, just like SharePoint OOB REST services seem to be able to.