It feels VERY good in the hand. It's very light (but still not too light) and thin. The curved edges definitely help to make it feel smaller. I probably spent a total of four minutes just fondling them and getting high off the colors. Speaking of the colors, my favorites on the Nanos would be silver (the black click wheel made it look a lot less basic and a lot more hell-yes), blue, and green. The build quality was probably the best of any iPod I've used yet. To put an end to this paragraph, it looks and feels very good in the hand (the curved click wheel wasn't annoying at all, despite my expectations).
So how's the interface on that awkward long screen? Really good. The spacious menus made navigating much easier. They also smoothed over all the animations, such as that sliding animation between screens. I definitely prefer it to the interface of previous iPods.
Cover flow was very good on the new Nano. It's definitely something I would use. From anywhere under "Music" you can turn the iPod on it's side and get to it. If you do it on the Now Playing screen, there's also an animation that rotates the album art 180º and shrinks it into cover flow. Then you scroll.
I like that because it's a nice way to get right from Now Playing to scrolling by album. The accelerometer is responsive and quick, so there is hardly any turn-and-wait. You do have to turn it a pretty good amount though, but that's actually a good thing because it prevents accidental-cover flow. And cover flow has really been improved over what was in the previous iPods. Album art loads much faster and there is a lot less lag. The animations are smoother and scrolling is much easier. You can also scroll by letter by scrolling very fast, which I found to be very useful. And I know it wasn't like that just from the store having a small library, because on the new Classics it is still just as laggy and slow as ever, and all the iPods in the store have the same content on them. So essentially they took something that was totally useless before and made it pretty great. Something you might not know though is that when it's rotated, the buttons on the click wheel don't rotate their functions. So Menu is on the left, fast forward is on the top, rewind is on the bottom, and play/pause is on the right. It's not nearly as awkward as you'd think, though.
By the way, the new Now Playing screen is very pretty. I like the big album art covering the top, it looks very good (though I bet it looks kinda ugly when you play songs that don't have the art) and how they fit everything else on bottom without making it look cramped. Text is small, but readable. Animations (such as when you press the center button to change functions) are smooth here as well. I also like how they worked in Genius. For those who don't know, holding down the center button while on Now Playing brings up a menu on the top where you can choose to add that song to the On-the-Go Playlist or make a Genius playlist out of it) The Nano gets an A+.
And while I'm here, I'll say a few words about the other new iPods. The Classic is pretty pointless, as I've said before. Plus, it's an insult to everyone who owns the old Classic (me). Despite the nice improvements in the iPod Nano, you don't get any interface changes (no smooth animations), cover flow is still useless (I know it doesn't have an accelerometer, but they could have smoothed the animations and given it letter-scrolling), Genius seems out of place (if you hold the button on Now-Playing you don't get a pretty menu on top, it takes you to a whole new menu where you can't see the now-playing screen where you then choose what you want to do with that song), and it has support for the remote feature on the new iPod in-ear headphones. Why's the last one bad? Those of us with the old Classic (which is essentially exactly the same) are taunted with more (for us 80gbers) space and the headphone support and the lazy addition of Genius for the same money we paid for our 80gb iPods, and those with 160gb now have a less valuable iPod because the 120 is closer to 160 for the same cash the 80 once was. That sounds stupid, but when you pay $350 for an MP3 player, you want it to retain value for a while. Plus, the 160gbers, even if they're OK with paying another $250 for the unexciting new Classic, lose 40gb of space. I think we would've been better off if the Classic was left alone and if the new headphones used an adapter or something to connect through the dock connector (that way everyone with a recent iPod could use the remote).
The touch is cool. It's not super different from the old one. The thinness is very noticeable though. It's extremely thin. The back looks neat with the curved edges. It's pretty much the same as the old one, except for the built in Nike+iPod and the speaker. Oh yeah, and the speaker hardly makes it worth getting to replace a current touch. I guess it would be convenient if you forgot your headphones and wanted to put it right in your ear, but otherwise it has little purpose.