It's reasonably fast, has a shitton of (actually pretty good) editing functions via plugins and gets the job done. I just wish it had an option to "repair" gifs that have a wrong frame rate set.
I really like Honeyview. A few clicks in the settings window and its interface is gone, all it shows is the image, and supports hotkeys to switch to next\prev image or zoom. I don't want to ask for more.