The biggest selling point is the Zune Pass. I had quite a bit of non-drm muisc before the zune but this gives me access to essentiallyl every song they have. For $15/mo you get unlimited music on 2x computers and 3x devices. This is great because our listening interests vary every week. From country to pop, from alternative to techno, unlimited music is a great solution.
Now they have improved it by offering 10 free "buys" per month. Every month you get 10 free buys with your Zune pass.
The biggest drawback is - it is a zune. I can stop at any gas station in middle america and find an iPod case or iPod charger. If I want zune accessories my options are considerably more limited.
Recently the engadget guys mentioned something that i'm sure was common knowledge to everyone but a realization to me. Apple wrote software that runs on both an iPhone or an iPod touch. Same software, same interface, different uses. One is a media player, one is a media player that can also make calls. The Zune is nothing like Windows Mobile. Rather than utilize windows media player and reference windows mobile they wrote a completely different operating system for the device and a new media playing product for the computer.