The stock camera app that we see on Nexus devices has been one that Google keeps having difficulties. Back in the day of Ice Cream Sandwich the camera app from Google was horrible but since then it has improved. Despite all the efforts there are still some issues that needed the attention of Google.
Rumors are that Google is working on a new camera app and it will be available as a separate app for KitKat and above devices (possibly trough Google Play). This new camera app will feature an accurate viewfinder (what do you see on the screen is what the camera will capture) and new features like filters (you will be able to add third party filters) or even features like blur the background to give that depth of field effect like the HTC Duo Camera gives or the Galaxy S5 via software). The app will also improve Panorama shots and Photo Sphere.
If Google make this right is one more positive value for Nexus devices specially the Nexus 5.
Source: Android and Me