what do you find to be the biggest difference
The Windows 8 tiles take some getting used to, although there's a tile that takes you to the old-style desktop. The "Start" button missing on the desktop is a real nuisance. Its omission makes things harder to find.
Also there are hidden menus in 8 that I don't like. And having to hover your cursor on the right top edge of the screen to get to settings, power and such is a nuisance too.
Classic Shell gives users who are used to XP/Vista/7 an easy way to circumvent those things so they can get "up and running" quickly. Later you can play with Windows 8 - a lot of trial and error as there are often no obvious instructions - and get used to it if you want.
Classic Shell is a must, as far as I'm concerned, for an easy transition.
And, as I said, a separate download of Windows Live Mail fixes up the email fine, but you shouldn't have to do that. The mail program built into 8 is annoying, with again hidden stuff, and (to me anyway) counter-intuitive navigating.
I wouldn't be afraid of a computer with Windows 8 now, but 7 would still be my first choice.