Preview is a good option, but you should consider Quick Look, which offers almost everything you want, is built-in, and is available all the time.
It’s dead simple: Hit
Command-A to select all the images in a folder, then
Command-Option-Space to bring Quick Look up in full-screen mode. If you want to zoom in more, you can use the zoom feature which is built-in to Mac OS X: While holding
Control, scroll up to zoom in, and scroll down to zoom out. You may need to enable zoom in Preferences; I don’t recall if it’s enabled by default. It’s simple enough: System Preferences -> Trackpad -> Screen Zoom.
Quick Look can show you one image at a time, and it also has an Index Sheet mode, which shows you thumbnails of all the images you selected. You can navigate with the arrow keys, or with the usual swipe gestures on your trackpad or mouse. It even works with RAWs. Give it a shot! I think you’ll be very pleased with what it can do.