My initial impressions are positive. I haven't had the opportunity to do much with it yet, but I did play around with Excel 2007, and I'm much happier with the layout and appearance. I'd say it's lots more intuitive, and from an aesthetic standpoint, it's worlds better. It will take some getting used to, for sure.
Only time will tell whether the almost-$300 I spent was worth it. But I've loved Office since I first set fingertips on it, and I think that upgrading from a 5-year-old version probably isn't a bad move.