I just want something that lets me zoom in and out with the mouse wheel, lets me run multiple instances, and is easy to use. Gliv fits the bill for that, and you can easily install it directly with apt. However, it is not currently maintained.
GPicView, the default viewer of LXDE, was also evaluated, but it was found to use the mouse wheel to scroll between images, which is not my preferred UI option. Therefore GPicView is not my preferred choice.
I eventually discovered Eye of Gnome (Eog), which is better than Gliv as it allows you to turn the mouse wheel the correct way to zoom in and out (that matches Google Earth and Qgis) and also names its windows directly after the image, which is handy if you have a lot of them open. Eog is therefore my preferred image viewer on my Linux computers.