I wanted so much to hate Windows 8 and I will even admit to hoping that its the new Vista, but in truth, I kind of like it.
I have bought the Stardock suite of Apps and so I got it to look a bit more like Windows 7 but this can be done just as well ( mostly ) with free apps.
Speed-wise, I would say there is ZERO difference in the running of any games or apps but I have found a number of issues that I have found to be a bit of a PITA.
Speedfan, while it works, I cannot dump it into the StartUp Folder to get it to load up on startup.
Virtual Clone CD. On a fresh install its good, but upgrading from W7, it wanted me to reinstall. A minor issue of course.
A couple of older Benchmark apps dont work either.
Again, these are all silly things, but when you use certain apps, it gets annoying when you can no longer use them.