Going from W7 H.P. to W8 was a breeze. If you don't mind some 'minor' changes, loss of START MENU and the new Start Screen, once you get to the DESKTOP you don't know if it is W7 or W8. There are quite a few programs that will make W8 work just like W7 with respect to by-passing the Start Screen and going direct to desktop. However there are some 'gotcha's' along the way. Some programs will not work at all, some need to be re-installed. Run the W8 Advisor on the MS site to determine which ones these might be, but that app is not foolproof, you might still find a surprise.
My wife was upgraded first and she hit some game snags and had some minor problems. Game company (GameHouse) is slowly updating the games that they can to make them work on W8. Other than that, she seems able to navigate quite easily, and I've not disabled the Start Screen.
One BIG hit for us was Norton Ghost 15, doesn't work... on W8. A new product does, SSR2013, but there are other back-up alternatives that work and are cheaper for more than one computer.
GO FOR IT!!!