But it still supports the old file formats and there will be functionality added to Office XP and Office 2003 so they can 'take advantage' of the features and smaller file sizes the new formats benefit from.
As for it being more complicated, I believe the whole point of the new interface is to make it easier to use.
Apparantly the first version of Office had 150 functions whereas 2003 has some 15,000 but using essentially the same menu structure means most are hard to find and never used. The new layout is meant to address these issues.
I like it, but then I'm easily pleased and often don't want to see past the nice new colour schemes lol.