2010 is a lot like 2007. The exception is Outlook that gained the ribbon too (in 2007 Outlook was the only app without the ribbon).
I have been using 2010 for about 6 months, and actually I think is MS best Office product ever. And that is a lot to say, since I also use open office on my work laptop.
About being slow, I would not know, since I am running the beta at home. It crashed only once, and my work email was configured from home without direct access to AD, which is a super big plus. I like the interface of Outlook so much, that I don't read much of my email at work, but I do at home. It takes me 10 minutes to go thru my email, compared to an hour at work.
The default view is by date by conversation, but it integrates with windows search so well, that it can list the emails from other folders.
Again, I am running office 2010 at home with Windows 7. It seems to be develop for that OS, and i seriously doubt I would install 2010 in a PC not running 7. Since all machine that run Windows 7 also I consider that they should have not less than 2 year old hardware, office should run fine. I will install the technet RTM on my laptop this week and I will compare it with my desktop, but I already feel that my laptop is slow compared to my desktop (and the laptop has a Dual Core 2 Duo T6600).
The changes in the rest of the products are some polish on the interface, and a lot of internal changes. I think that overall the xml engine works better in 2010 than in 2007. I don't know if it is more compatible with other suites like OpenOffice though