Just got mine today, I've got the old one as well.
Early days but it is VASTLY better in every way.
Build quality, it feels and looks a much higher quality device, no flexing or creaking. The buttons on the side feel more solid. It looks a fair bit smaller.
The screen and touch response are noticeably better, the image quality is obviously higher but its also brighter and more vibrant. The touch response on my old one was quite iffy, this one is excellent, very accurate, even typing on the old one was frustrating, its a lot better on this.
The performance is vastly better, the old one was pretty sluggish at times, this one feels as snappy as a Nexus 4, which is how it should be.
Obviously its got a camera too but its not the best, but still.
So far its a cracking little device, well worth the upgrade over the original IMO.
Still doesn't replace the chromebook though for its desktop class browser and real keyboard and trackpad, but I didn't expect it to. They are great compliments for one another.