For me, the biggest make or break for any mp3 player is its versatility, and iPod fails this test. You can't drag and drop music, plug it into multiple computers, transfer music back to the computer if your computer dies and loses all the music, you need to install software to use it so you can't at work, etc.
I realize there are workarounds to most or all of these, but I hate the idea of having a player that treats me like a criminal and having to jump through so many hoops to do basic things.
My RCA Lyra mounts as a hard drive and can build its own iD3 database, so you can drag and drop music to and from any computer without installing any software. It doesn't have a sexy scroll wheel, but versatility and compatibility wins out for me.