My new laptop has Windows 8 on it. It took a little bit of getting used to because a lot of the shortcuts are a little different and the start menu pretty much took me aback on its own. But I got used to it after a while.
I heard that there are some computer 'tricks' that you could do on Windows XP and Windows 7 but apparently you can't do them on Windows 8. I haven't personally experienced anything of the sort so far.
One of the little things that really bugged me was that you pretty much need a Microsoft account to download anything from the store or use the Calendar and mail app.
>>3 I'm pretty sure you can install programs even if they aren't in the Windows store. For example, my text encryption program isn't on the Windows store but I've been able to install it anyway. Not sure why you can't play Slender though.