I've had an iPod Touch since the first generation. Personally, I find it to be more revolutionary than the iPod. Why? Multi-touch is everything. It is on par with the iPhone in technology, since they both have basically the same thing. And with the advent of the new front-facing camera, aft HD camera, it's a great edition to the iPod line.
This new iPod supports the same Apple A4 chip (~1Ghz) as found in the iPad, iPhone4, and now the AppleTV. This means zippy downloads, smooth scrolling gameplay, and support for more processor-heavy applications.
The new camera is only 720p, but that is still not bad. Sure it's not 1080p, but I don't really find any sense in placing something that powerful in a handheld device. Hands are shaky, and 1080p looks terrible when handheld. Any movement can be easily detected, so the 720p should be more than enough.
The slim trim and styling of the iPod is no revolutionary, but I'm still amazed that they can make it smaller and smaller every year. Mine must look like a brick against this new one.
Here's a tl;dr version:
Size - smaller than ever!
Battery life - 40 hours audio and 7 hours of video sounds spectacular!
Retina display - I haven't personally tried it, but have heard reviews about it and it sounds fantastic :D
Price - $229 for 8GB isn't so bad, but I think most people will spur for the $299 32GB version. I know I would.
Camera - forward and aft facing cameras. 720 support is awesome.
Chip - 1GHz Apple A4 sounds zippy and quick!
Included headphones - meh; probably one of the worst headphones ever.
Same style - shouldn't they have updated the design?