How would you describe an image viewer beyond the obvious?

How would you describe an image viewer beyond the obvious?
What do you believe makes a good image viewer?
It is feature rich? Minimal? Customizable? What makes a good image viewer to you?

Well then there's nothing to explain. Image viewers view images. The more images they view while still being speedy the better the viewer. Anything else is purely subjective.

Animations are animated.

It views images and lets me zoom in super close.

Let's me choose down-scaling and up-scaling algorithm.
Has accessible shortcuts for fit image, 100% "zoom", next image in folder, previous image in folder and movement when zoomed-in
Performance (particularly with gifs).

eom does some of that well enough, but it has problems with bigger gifs and some of its shortcuts are not accessible enough (awkward key combinations, next image doesn't work when zoomed in).

I didn't bother to look for something better, so if you know of something I'd appreciated it.

The default image viewer in GNOME werks fine.

Anything beyond viewing images in an image viewer is bloat. If you want to edit images use an image editor.

OK, I should elaborate a bit. I mean anything that goes beyond doing more with images than viewing them. Any feature that allows to better view images is not bloat. Like being able to open multiple files at once and then flip through them, zoom, have thumbnails, all that stuff is good because it makes the viewing better. What I mean by bloat are editing features like changing color saturation, or some sort of image organization features and so on. If you really need them provide an interface for plugins so people can choose their own bloat.

That's why OP is talking about image viewer. There are quite a few things to consider when choosing an image viewer that only views images.

What would be nice is if the image viewer had fast and accessible tagging (preferably using the filename). Something like t -> menu with most used tags shows up, and then you could either choose one with Alt-n or start writing, which would filter the tags, and enter to add the tag.
Mass tagging/operations would be nice too.
It should be able to display everything with certain tag or -(i)name/regex match, including in subfolders.
It should use a library designed for displaying fast image sequences for cases when it wants to display fast image sequences (i.e. animated gifs) (ability to pause gifs would be nice). Or alternatively, it should let the user define command for viewing gifs and show just the first frame (in which case it could support videos too, showing just the thumbnail)