IrfanView is trying to create new and/or interesting features in its own way, unlike some other graphic viewers, which whole "creativity" is based on feature cloning, stealing of ideas and whole dialogs from ACDSee and/or IrfanView!
(for example: XnView is stealing/cloning features and whole dialogs from IrfanView, since 5+ years).
IrfanView was the first Windows graphic viewer WORLDWIDE with Multiple (animated) GIF support.
One of the first graphic viewers WORLDWIDE with Multipage TIF support.
The first graphic viewer WORLDWIDE with Multiple ICO support.
IrfanView Features
Many supported file formats
Thumbnail/preview option
Slideshow (save slideshow as EXE/SCR or burn it to CD)
Show EXIF/IPTC/Comment text in Slideshow/Fullscreen etc.