Imagina is an interesting image processor and viewer. It's not crammed with features - there are no drawing tools, few of the usual effects - but what you do get is very professional, and much better implemented than in most of the free competition.
The thumbnail browser opens with a "3D Desktop" view of your images, for instance (including many RAW formats via dcraw), each picture dropping like a real photo on a marble desk. If this is a little too gimmicky then you can switch to a regular 2D view instead, or browse your picture full-screen.
The pictures look great with the default settings, but if you need fine control then Imagina allows you to configure colour management (rendering intent, quality, enable/ disable gamut checking, relative colorimetric etc), and optionally enable smoothing when zooming in and out.
Navigating around an image follows the usual pattern of spinning the mouse wheel to zoom in and out, clicking and dragging to pan, although hardware rendering support means this all works very smoothly. Click, drag and release, say, and the image gently decelerates rather than stopping immediately.
You can rotate, flip, resize and crop an image, of course, but even here there are extras. The program is able to batch resize a group of images in a single operation, the Crop tool supports fixed as well as custom aspect ratios, and you can straighten an image by rotating it to match an arbitrary line.
The Effects tab provides various ways to fix your image by tweaking brightness, contrast and colours, or using custom filters to smooth your photo or reduce noise. There's typically a lot of control, so for instance clicking "Reduce Noise" doesn't just apply a single canned effect: you're able to choose the type of noise based on the image source (camera type, JPEG artefacts, half-tone scans, dust and scratches), and then tune Imagina's settings even further for the best possible results.
Other tools include a "Period Style" option to make an image look like an old photo (much more than just a sepia filter), a simple Properties view of photo metadata and the ability to view GPS locations on Bing or Google maps.
Imagina isn't in any sense a complete image editor (there are no drawing tools, few filters, not even a "sharpen"). But its viewer works well, there are some smart correction tools, and it's generally easy to use.