So, personally, I liked it well enough at first but I've noticed a number of things that have irked me enough that I doubt I'll be buying the release before SP1.
First: The hot corners/edges. I've found when I play games in a borderless window (a nice way to play with dual monitors) I hit the hot-corners/edges and bring up menus or switch into the start menu. Not something that's unfixable but it's annoying as hell, and I encounter it enough that I am going to put 7 back on my PC for this reason alone.
Getting stuck in metro. On my dual monitor setup, it's fairly easy to shift back to desktop by clicking the other monitor, however I've found that if I open a metro app then metro will stay open when I click off screen, even if I go back to the main menu. It's annoying (especially when combined with the above issue with hot corners).
I really can't say I've used the metro UI much, but I don't find it useful, and it limits multitasking capability of the computer to use the metro apps. For me, it's just an extra click between me and using the computer. I find when I open a file that pops up in a metro app (such as an image) I would rather just close it and open it in something else, and closing the metro app is a multistep process that isn't really natural to me (especially after the context shift from desktop land).
It crashes alot more in games, which is almost certainly due to drivers, however it's pushing me back to windows 7 now, rather than keeping me on windows 8.
I do really like the boot time. It boots faster from a 7200RPM hdd than Windows7 from my SSD, (though apps aren't ready right away).
Overall, the OS is quite snappy and all that; I just find it to be a pain to use, despite trying my best to like it. Sure, i could probably work around some of my issues, but there isn't much of a payoff in the end so why bother.