I'll give you my opinion I had a zune for a week.
First I'll tell you I don't presently have an Ipod but I had a 5G, sold it for the Zen M. I would'nt mind getting a 5.5g now that they've improved the screen. The Zune was an OK player but it had faults. First no Customizable EQ, same Issue the Ipod's have had. The Zen's Customizable EQ goes along way in Sound Quality. The Zune's preset never had one that sounded best, but the overall sound was comparable to the Ipod. However mine made audible clicks and pops between tracks, it was not silent, I have seen some people remark thiers did as well so it might be inherent thru the device. The Interface was pretty, but did require alot of back presses to move around. And I agree with the posters above, how often will you be staring at Artwork. The Video feature is where the zune falls down. It only supports .wmv. The Software will convert (after a long process) .mp4 and H264, but it only natively plays .wmv. And it's .wmv in very strict criteria. 320x240 only with bitrate restrictions, wma audio track. Vary from those restrictions and the file has to convert. >WMV files take along time to encode, and there's only a few encoders that the machine played the vids from without encoding, namely WME9 , and Winavi. One thing the Ipod and Zen have going for it is a dearth of good encoders. The Thing I miss about not having an Ipod is Itunes Intergration, I simply liked Itunes better than anything I've used, I still use Itunes on my Mini, but the problem I had is I saved in Lossless format, but I want to save in a lossy format on the Itunes and there was simply no way to do this.