Viewer2 may not be the most full-featured photo viewer in the world, but is certainly an original one.
With Viewer2 you can browse your photo collection in thumbnails that can be freely rearranged on your screen. First of all, select the photo folder you want Viewer2 to display. Then double click any of the thumbnails and you'll see that photo in full screen.
You can zoom in and out with the mouse wheel, and go back or forward in the photo folder with the PageUp and PageDown keys. Also, right-clicking on any full-screen image will show a filmstrip with all the images included in that folder.
Some functions included in Viewer2 are photo tagging, image rotation and marking specific photos as favorites. Other than that, Viewer2 doesn't feature any other tools or options, and it's not even embedded with Windows Explorer.
As much as it's an original photo viewer, Viewer2 may not be that useful for the power user.