I'm an owner, and am VERY satisfied with my device.
The complaints I have are minor. It can take a little bit for it to connect to a wifi network, but that's not a huge deal. Sometimes, it's a little sensitive in registering taps, but that's once again not a big issue. The carousel is a little too speedy for my liking, but I rarely use it, and when I do, it's usually just to open the very most recent thing I've opened.
I haven't noticed any real speed issues with it; at least, nothing show-stopping. Books read fine. If you're trying to fly through a bunch of pages like you're thumbing through a book to find a certain page, sure, it can slow down there, but I almost never do that. Games & streaming content perform perfectly.
I didn't notice any real issue with the browser; I was able to load websites faster on my Kindle than a local iPad owner, over the same wifi connection.
Typing is easy for me; in landscape mode it can be slightly difficult, but not unusable. I usually use portrait mode, anyway.
The lack of physical volume controls doesn't bother me at all. It's stupid-easy to get to, and keeps me from accidentally raising/lowering volume.
I do wish I could change the lock screen photo(s) easily, but that's not exactly important.
Regarding the lock/power button, I have NEVER accidentally tripped it, and I'm using it on a daily basis in a variety of situations.
If you look at reviews on Amazon, there are a good number of 4 and 5 star reviews; more than 3 or less.