iTunes was awesome on Windows when it came out (until about 4.0?). Compared to its contemporaries, Music Match, which was a bloated piece of junk, and Winamp 2.x which while awesome, had a steep learning curve to get really useful (J for the win) and had an extremely unpleasant UI.
It forced a bundled QuickTime install (still does I believe), and back then, it tried hard to become the default media player on your system (even reverting your "no" choice after updates). This led many people to remove QuickTime, only to discover now their iTunes refused to work. It would fail halfway through sync's and upgrades of iDevices routinely, had a generally pretty buggy interface that wasn't very responsive most of the time. It's iDevice backup process was cumbersome for normal users, and often failed without the user knowing (leading to very upset individuals when they needed to restore but couldn't).
Now it seems every new version redesigns the UI in major ways, causing even long term users to not know what to click, etc...
If you really just listen to music, maybe it's fine. For all other purposes, it was/is horrible, however I can't complain because it generated quite a lot of work for my side repair/contract business back then.
I had whatever version was around when the video ipods came around (and a bodgy bit of hardware that was). I couldn't sort videos the way I wanted to - itunes says that that file extension means "tv episode" instead of "movie"? Sorry, it's a tv episode. Not to mention the terrible UI with tiny targets that doesn't blend in with the user's desktop theming. Maybe that was v4+, but all I remember is hating to use itunes (including managing updates as already mentioned)
The software that went with Microsoft's Zune media player was amazingly good. Sadly, even though it was available separate from the Zune hardware, almost nobody downloaded and tried it.
