Let us start with the obvious things. The Tab UI is awesome. I have never liked the Firefox Tab UI. I think the IE Tab UI looks good, but they (we) never really nailed all the little quirks. Putting it up in the non-client area seems like such a no-brainer now. The UI is snappy, the animations are good looking, but subtle enough not to get in the way of using the product.
The MFU with thumbnails on the new-tab page is nice, though I wish it was more than just the top nine pages. I find it odd that I like it so much because I was really against doing something like this for IE (but I also never thought it could be made so fast in IE). I love the history-as-a-webpage feature. I am a little disappointed that I can not find a shortcut key to get to bookmarks. I don't want to take up screen space by having the bookmarks bar visible (though it is nice UI if you do turn it on). I know I can just type the name of the bookmark in the address bar, but I actually have long lists of bookmarks that I like to visit every day in a specific order. Instead I use CTRL+T to get a new tab then click the bookmark button.
I love the simplicity. We tried to make IE7 simple by getting rid of the menu bars and re-working things into the command bar. Chrome takes it all the way though.
The only UI I think looks wonky is the little pop-up in the bottom corner of the screen that appears when you hover over links. But I do like the little drop-down find box.
And of course, it would be nice if it worked with the ajax-y features of Facebook and Netflix.
