I'll gear this review to 2 types of people: current Zune owners who are considering an upgrade, and people trying to decide between a Zune and an iPod. (There are other players worth considering out there, like the Sony Walkman X, but I hope this gives you enough info to make an informed decision of the Zune vs players other than the iPod line as well.)
Zune and iPod: Most people compare the Zune to the Touch, but after seeing how slim and surprisingly small and light it is, I consider it to be a rather unique hybrid that combines qualities of both the Touch and the Nano. It's very colorful and lovely OLED screen is slightly smaller than the touch screen, but the player itself feels quite a bit smaller and lighter. It weighs about 2/3 as much, and is noticeably smaller in width and height, while being just a hair thicker.