As someone who thought the same (stock was enough for me) until I had some free time and switched, here are some things I'm really enjoying, in no particular order:

- Format support: EPUB, CBR/CBZ (comics, graphic novels), PDF

- Dark mode

- Fully programmable gestures and shortcuts

- Automatically syncs with my readeck instance (think readitlater/instapaper) to dowload the articles I save for example here on HN

- Calibre integration over wifi

- RSS/Atom

- Custom dictionaries

If you are into manga, there is an extension for directly downloading them on the device

I'm really happy I made the switch.

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dml2135 3 hours ago | parent [-]

What's the point of Dark mode on an eink screen?

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DarkStar851 3 hours ago | parent | next [-]

For some people it's less eye straining if they're reading at night, doesn't help for me personally, but it's a popular feature

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CWuestefeld 2 hours ago | parent | prev | next [-]

Because most of the page is dark, with light only coming from the text, the total light emitted is much less. That makes it less annoying to my wife, when I'm reading before going to sleep.

	▲	BenjiWiebe 8 minutes ago \| parent [-]
		Eink doesn't emit light.

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jabroni_salad 3 hours ago | parent | prev [-]

I have no idea but users seem to like it despite all the ghosting.

The reason I use koreader is because it can sync my progress on disparate devices. I have a normal sized kobo and also a phone sized viwoods eink device.