LilyView is a program that comes as an alternative to using Mac's Preview application for opening pictures on your computer. The utility works with a wide variety of image formats, supports drag-and-drop actions, and lets you choose between multiple view modes.
You can import folders containing images or single files. Simply drag-and-drop them over the app's interface and you can start browsing your image collection within moments. The app lets you use your trackpad or arrow keys to head to the next picture, toggle fullscreen mode anytime you like, and even rotate the imported photos.
LilyView also provides you with a quick way to print photos. Just hit the Command+P keys, configuring the printing settings according to your needs, and that's it.
Still, many of the aforementioned flaws can also be found in Mac's Preview tool (which comes by default with the OS) and many other utilities which are free.
In my opinion, you should first test the program on your Mac and then decide if it's worth buying its full version or not. Personally, I prefer using Preview as it offers me all of the advantages I need from an image viewer.