I have a Gen 1 Zune (30 gb) and it's still going strong three years later.
The Zune software has improved some, but still is somewhat lacking, but is WAY better than I tunes. However, there are ITunes alternatives, and to date, none for the Zune.
The sound quality of the Zune is really good, better than every IPOD I have heard, but not better than my cheap Rio Forge player.
Zune battery life is just ok, and will only last about 4-5 hours on with moderate video and screen use, though the new ones may be better.
Formatting video for the Zune can be a PIA, but it will play most mp4, and WMA files, after conversion.
I have not used the Zune music service, or the WiFi very much, so I can't really comment on that.
Accessories for the Zune are limited, but more are available now than when it first came out. If you want to interface with a car stereo and have control over the player, then Ithe IPOD is about the only game in town. If you have an AUX input, then any player with a 1/8" jack will work, but you must use the player itself for functions.
If all you want is a music jukebox, then get a cheap Sansa or IPOD Nano, or any other cheap player.
If you need video, then the new Zune HD looks nice.