As a long-time Irfan View user, I can definitely say that I've never seen a better graphics viewer, even without all the recently added extras. The additional features only add to its value. For quick viewing, navigating through multiple image and sound files, and performing lightning-quick batch conversions, nothing compares. I've used a lot of image viewers over the years, but Irfan View is simply the best in its category. Go get it.
Pros: Lightning quick image viewing, excellent multimedia support for most formats, free
Cons: For graphics viewing only - no manipulation/editing tools