I'm always skeptical of video apps on my iPhone. Perhaps coming from the video editing world of Final Cut Pro I have a hard time believing that the same things can be done on a device that fits in my pocket.
I like how quickly and easily you can apply different effects and get a video out to YouTube or Facebook for sharing. The novelty of editing video with filters and effects wears off for me much quicker than photo editing does simply because it takes longer - but Game Your Video does a great job of keeping the processing / rendering time down and allows you to preview a lot of the effects live on your video.
It works decent enough on my iPhone 4. I'd imagine on a newer device the rendering/export times would only decrease.