HTC Camera combines plenty of adjustable manual features (ISO, auto white balance, exposure etc), lots of pre- and post-shot filters, and some cool selfie retouch options. On top of that, it's very easy to use.
The results depend on the model of your phone. On an HTC One M7, the photo quality from the rear-facing camera was excellent but poor from the front-facing one.
While it won't suit pro photographers, HTC Camera is a solid all rounder that is top of the pile as far as stock camera apps go.