After reviewing hundreds of camera apps it's hard to not get jaded. They are often endless variations on a theme, all doing the work of shooting and editing OK, but not bringing much new to the game.
Camu (free) hits the ground with a fresh approach and some new features. For example, its filters can be applied before and after you take a photo or video. You swipe the screen to get a new filter, and you swipe up or down to increase the effect or decrease it. The filters are never over the top, and really can make your photo or video more interesting.
Speaking of video, you hold the photo button down to shoot video, and release when you are done. Filters work both before (for a preview) and after as it is with stills.
Real-time collage is an interesting idea. You split the screen and take a picture, then your next picture goes on the other side of the split. It's faster than going to another photo editor and creating a collage after the fact. You can use your finger to drag the split marker around so it can be vertical, horizontal or at an angle.