Enhanced Image Viewer was removed from Chrome Web Store recently and is no longer available. It was a very popular extension. I think its features are easy to implement:
Zoom image with mouse wheel, without having to press Ctrl.
Pan images by holding left mouse button and dragging them.
Actually, it comes with more features and customization. But this basic stuff is the thing I use and miss most. Other features I can live without. Can you please give us this?