After having used windows 8 for a few months all customized in desktop mode, I enjoy it...as it isn't that much different. The new start screen, is, as jerzey has said, designed primarily for touch enabled devices. It is an action within the company to defragment their services, as well as a target towards their largest consumer base, "The Standard User". As a good number of us here are what is considered "Power Users", if only on the low end, 5 minutes of searching and 5 minutes of customization and you have Win 8 looking and working a traditional desktop mode. The actual functionality has only got better since the older systems.
Win XP -> Vista - Most people hate this step as Vista is fairly known to be a pile of poop, but this was a huge step towards making things pretty as far as operating systems go. Sure there were a few problems, and many an annoying pop-up, but it was a good step in a right direction.
Vista -> Win 7 - This, as it seems to me, was essentially fixing everything they did wrong with vista. Having used both, and xp, for large amounts of time, I am a huge fan of 7. It does most things right, and as a desktop operating system was straight solid.
7 -> 8 - I have only used 8 for a couple months, really, but am liking it as a desktop operating system. I customized everything to give me the traditional desktop feel and it is good. This step did introduce the new start menu and I have to say I love the idea. I had to set up a new 27 in touch all-in-one for my aunt and it is pretty spectacular, for a non-power user. The touch interface with the new start is kinda awesome.
The different steps were necessary, and as crane and jerzey have both objectively pointed out, it is definitely the next logical step of progression. That being said, we should all be using linux. It is the most widely used operating system on computing devices.