I was thinking last night (sorry)... Reviews & recommendations should probably be different types of events, no? Since reviews can be negative, they wouldn't really fit into a recommendation category. Or for example, a scenerio that's likely to arise at some point of, 'this app is "meh" but it's what is available so I still recommend it'. 

Reviews should probably have their own NIP & event kinds since you can review many things & you don't necessarily want to have all of those tied together, such as reviews of apps vs movies vs recipes. 

Just food for thought for anyone interested.