I suppose the key difference is that some people want just a read-only image viewer that traverses a directory, while others want a photo viewer, or image metadata editor, or photo management system. I haven't used Windows' default image viewer in ages, but I recall when I used it, rotating an image actually rotated the image, as in it changed the orientation header of JPEG files and rewrote the files. This is why I have trust issues. If even image viewers can't just view the image, how can I possibly trust the software that drives cars, flies planes, or does the banking?
Not really the difference in context of IrfanView which is also just an image viewer.
I tried JpegView, but it’s lacking several features I use in IV, and stuff I commonly do in IV is harder to do, so for me IV is a clear and easy winner. Performance is a little better, but not in a way I’d actually care about (mainly superfast skipping through images is slightly faster)
* Settings in one place, that way I could have probably easily found out how to remove the annoying zoom-features.
* Batch conversion
* Slideshow: Add files/folders, not just a textfile or folder
* Slideshow: More options in general, e.g. random or unique random.
I do think it's odd to expect an image viewer to be able to do batch conversion, though. That's what I meant by a read-only image viewer.