My wife and I both love our Kobos!
It's a basic ereader with no frills...no wi-fi, no 3G, you download books to your computer and then to the Kobo. The payoff for this featurelessness is minimal size and weight, making it very light and about as small as you'll get with a 6" screen.
This is not a good device for reading PDFs, which are not really designed for ebook readers with 6" screens. You want ePub, which allows you to resize the text.
The Kobo comes with 100 classics pre-loaded. You can buy books from Borders, Kobobooks, Smashwords, and non-DRMed ePubs from B&N, Sony, and others. If you want a top-notch ebook library management program, download the free "calibre" program. It will recognize the Kobo automatically and lets you organize your library YOUR way.
I'm sorry the one-star reviewer had problems, and I wish I knew where he lived so I could grab his Kobo out of the trash!
EDITED TO ADD: Being able to log onto my local library's webpage and check out ebooks is pretty cool!