Improved: gesture control. I find it difficult meanwhile *not* to swipe on other touch screen devices. Especially swipe down to close is very nice and natural.
Navigation is nice if you own a car. I don't.

Things that are worse in comparison:
No copy-paste, except for a few text input fields. This is very annoying especially in the browser, where text input is fundamentally broken.
No cursor keys on the onscreen keyboard. The replacement (a lense) doesn't work in all applications... again, the browser is the most important application in which you cannot control the cursor position at all.
The display is the worst I've ever seen on a mobile phone, much worse than the wonderful display you enjoy on the N900. Color bleeding, shadows and stripes, purple tint, whatever... there's a whole thread about it.
Also lacking from the browser is the 'mouse over' mode you have in the N900, flash support of course, any way to edit bookmarks (actually, there's no such thing as bookmarks)...
There's no Jabber integration in the IM system.