Yeah the GUI isn't exactly current-millennia, but it's unbeaten on features. There are even basic colour correction tools inbuilt, you can copy chunks of an image straight into photoshop or whatever just by selecting an area and hitting ctrl-C (saving having to drag the whole image in there), and as long as the thumbnail previews have generated it can skip through fairly large images as fast as you can spin your mouse wheel (and wrap back around if you've enabled the setting). Irfan plus Pureref for transparent imageboard overlays is an indispensable combo to any sort of visual artist / 3D modeller.