Where the domain is all about apps, I'm not sure you need an apps sub-category. I'd also put videos and reviews about apps in the category of app that you're reviewing. You can use a tag for video and review if you want, but I'm not sure it's worth it.
My logic here is that "iPhone reviews" doesn't have the intent of looking for apps - they're looking for reviews of the phone. "iPhone videos" is the same - mostly people looking for videos about the iPhone. As you can see by the top results, Google understands this. "iPhone app reviews" or "iPhone app videos" aren't very high-volume terms, and certainly not the type of hierarchy that users would find useful. Whether the app has a video or not is definitely secondary to me as a user - the first is the type of app. In other words, I might brows productivity apps, but probably not random video apps.
I'm not going to get into a full keyword audit, but just make sure the home page describes broadly what you do. "Reviews of the Best iPhone Apps and Android Apps" seems to describe your site fairly well, but I'll leave that up to you. I will say, though, that you should have a regularly updated post for top app types on the "best ___ apps" in that app type.
I was saying that because most of your content seems to be app reviews or articles about new apps (there's not a hard distinction in customers' minds) you could structure it like this: