In my opinion, iTunes is a nice app. It has a killer media library and even has a built-in volume normalizer which is a big plus for me. It's not replaygain but better than nothing. The areas I think iTunes needs to improve on is the way it organizes your media library automatically unless you uncheck a certain checkbox. Plus as a ripper it needs to improve and give more options for file names because currently it limits the number of characters of file names to a ceratin number. It's even lower than 64 which is the max for the Joliet CD file system. I'm thinking they do that for iPod compatibility but I wouldn't know since I don't have one.
As far as their AAC encoder goes I think they should add VBR support like Nero's AAC encoder. And their MP3 encoder is just a joke and since they are pushing AAC anyway I doubt they'll do much with their MP3 encoder.