First of all, it is smaller than an AA battery. I don't know the exact dimensions or weight, but it seems like it would be very easy to use. Walt Mossburg from the Wall Street Journal said that it took him a long time to find it one time after he dropped it. It comes in silver or black with 4 GB of disk space for $79. The reason why Apple has been able to make the new shuffle the size that it is, is because they moved the playback and volume controls from the device itself to the headphones via Apple's new Earphones with Remote and Mic (included). I use these headphones with my iPod touch and the buttons are a nice way to play/pause, change the song, or adjust the volume without waking up the iPod. These controls are a perfect fit for the shuffle and it makes sense to take the controls out of the actual device.
The main new feature is something that has never been seen in an MP3 player before. It is called VoiceOver. Basically how it works is you press and hold the Play/Pause button on the headphones and the iPod will tell you the artist and song using text to speech technology. VoiceOver also works with multiple playlists and allows you to choose the playlist you want to listen to as they're being read out to you. I have not been able to try out this feature for myself, but I've listened to audio samples and they sound pretty good. It also supports 14 languages built in so "En la Noche" by iQuartet will not be pronounced wrong.
A couples of flaws I see in the device: since there are no controls on the iPod itself, the use of third party headphones, speakers, and car adapters are ruled out for now if you want to change songs. Supposedly Apple is in the works of releasing an adapter with controls to allow this. Hopefully it comes soon.
Unfortunately, my local Apple Store had not set up demo machines yet, so I have not used it or even seen it in person. However, based on photos, vides, reviews, and other information I have seen, it sounds like a great iPod, especially of you are already a fan of the previous shuffles.