I've now owned two Kindle devices in succession — one a 4th gen and more recently a 10th gen — and the use case for this device gets less impressive with every passing year. Not because I hate e-books, but because dedicated e-readers have been losing out to phones and Plain Old Tablets for a good half a decade or more now.
The main reason I started with a Kindle way back when was twofold: the e-ink display for comfortable reading, and the amazing battery life. This was before better battery chemistries and more casual charging and processors with far greater power efficiencies were the norm, so the Kindle felt like it had huge advantages over other devices. Now a $120 Android tablet gets an all-day charge and then some, and has all the advantages of a full-blown tablet on top of it.
This last point stands in stark contrast to the Kindle's laggy, draggy interface. This device has been out for I don't know how long now, and it still has such UI lag that half the time I end up with input queuing problems. Touches on the display end up getting sent to the wrong element, because the UI lags a step or more behind what's actually going on. Zooming on content is agonizing. There is no orientation sensor, so I can't read in landscape mode (something I really need to do when I have to zoom in on a PDF). And so on.
So much of the appeal of the Kindle was to have a dedicated device for reading, something where the other distractions present in such a device are either cut down or eliminated altogether. Ironic, then, that the one thing it's supposed to be good for, reading, it isn't very good at for a whole host of irritating little reasons.
To be fair, as long as I don't do anything other than turn pages and browse my collection, the Kindle isn't bad. But the minute I step out of that very narrow range of tasks, it becomes clunky. And it is far too easy to step out of that task range without realizing I have to.
It's depressing, really, that for what I paid for this thing, I could now get a tablet that does more, has at least as good battery life (maybe even more so), a slightly larger and even better display (e-ink is, I'm finding, overrated), and a system that I already know about and can work with more readily than the Kindle's own janky software. Buyer beware, and all that.