How Does It Look?
The most obvious change you will notice is the new look of the desktop and task bar. No icons are lined up as default on the left side of the desktop, and the only item present is the recycle bin, which is located in the bottom right corner. Also the Start Menu is quite different compared to how it used to be.
Of course, if you are the curmudgeonly sort who absolutely does not like the new style you can change to the classic 95/.../2000 look-and-feel by setting the Desktop and Start Menu themes to 'Classic'. Only a few interface details remain to make it apparent that you are using XP, but more about the control panel later.
The start menu immediately shows the most frequently used programs. To access all the other programs you need to click on "All Programs". This is just a more straightforward way of anticipating your actions then Windows 2000, which did a similar thing by limiting the views of menus and pull downs to most recent actions.