The term "image editor," in this case, is a little inaccurate. Irfanview is more of an image viewer. You can adjust things like the overall brightness or color balance of an issue, crop or rotate it, or save it in a different file format. But you can't work on particular parts of an image.
That having been said, Irfanview is one of the most useful pieces of freeware on my computer. It's a quick-loading, no-nonsense way to view any image file, and it's very useful for converting, say, TIFs into JPGs or what have you. It's a must-have, as far as I'm concerned.