Your music library will work perfectly fine in your zune. I have the first gen 30 GB model, and I've had no complaints. With the firmware/software updates they've done recently, it has made it alot better. M$ [or at least the zune team] doesn't want to leave the old gen people out. When new features come along, we get them first.
For example, wireless syncing. Have a wireless network? Let zune find it, get on it, connect to your pc, and get new songs that way. I've yet to perfect this, but to someone, this has got to be real useful. Something they did in a firmware update also helped with the battery life [i think this had to do with the FM transceiver being on ALL the time instead of just when you want radio.].
I've got a mass of music as well, and recently cleared my zune out from when I first got it and just dumped albums and albums and artists into it, taking a more scrutinized look at what went into my zune, because I was tired of skipping over things I didn't really listen to.
The zune charges via a usb cable [proprietary, of course], through your computer or even xbox 360, which obviously you can plug into and play your collection through your 360. I don't have any docks or anything, but some that I've seen are very nice and useful as well.
Zune? I recommend it. I had a 10GB zen micro or something like that before this, and I was happy with it. Now that I have the zune, I don't want anything else. I'm sticking to this mp3 player, possibly upgrading to next gen in the future.
Hope this helps