Been using it for quite a while and I have definitely used worse OSes.
On a desktop there is no difference between 8 and 7. In fact 8 runs better than 7...
On a tablet it runs very well if you get used to it. I have about 10 users using Surface Pros and they love it. It takes a bit of customization to get it working just right (which is an issue but it's one that is relatively easily overcome if you know what you are doing).