Tried it quickly for 10 minutes, then switched back, there was nothing really bad about it to me, but like you've said it feels like its got a bit too much going on, I think the appeal of Twitter from day one has been its simplicity, hence things like RT @ still being used more commonly than the Twitter Retweet function.
Will give it another go tomorrow, I guess they're trying to add more features to bring people back from using Twitter apps? and to use the site direct? I'd assume that more direct users would result in more impact for profitable features like promoted tweets and the newly announced promoted accounts - http://mashable.com/2010/09/27/promoted-accounts/
Interesting, I'd assumed from the people I follow and the number I see tweeting from apps it would be more like a 50-50 split, guess that's not a good representation of the general twitosphere then. I would also assume that the new interface has been heavily user tested, so will be interesting to see how it goes down over the next few days.
I love it, I wouldn't want the old interface back as it doesn't add enough, while this adds just the right amount (minus a auto URL shortener, and copy paste of images / vids, and full conversation lists rather than 1 post at a time)
It also means you leave your twitter stream alot less, which is definitely what I want to do, I want to see my tweets