Hi Katel, congratulations on your (almost) choice!
The newest firmware (like the operating system) of the KT has included the use of "shelves." You can make your own shelves and call them for instance mystery, thriller, biographies as per your examples. So you can categorise your books!
However, the shelves are very new and still very buggy and not very user friendly. You can only add them on the device itself, and you have to add books one by one from that shelf. You can't look at your entire library of books and say "This one goes on shelf A, this on on shelf C, this one on shelf B," etc. And there have been some cases where people have many shelves or lots and lots of books on shelves where to KT crashes or isn't able to properly sync them to the server...
Having said that, Kobo is still busy developing this feature and I expect to see them improve its functionality.
Be warned also, that the current firmware version that a new Kobo will upgrade to automatically (version 2.0.0) has some issues with slow page turns and displaying the wrong cover when in sleep mode of switched off (it displays the cover of the previous book instead of the current book -- if the previous book is the same as the current book the correct cover is displayed). Also some other issues... There are already fixes for most of the issues (not all) in a newer firmware (2.1.1), but this firmware is only officially out in Japan (you could install it manually if you'd want to). Kobo is intending to make a new firmware available everywhere very soon (whatever 'very soon' means).
Don't be frightened away though. The Kobo Touch is a really really really nice piece of hardware and I love it fiercely! You just have to be willing to bear with Kobo, forgive their bugs and be able to patiently wait for updates with fixes. Kobo DOES listen to their users with feature requests and bug reports (the implementation of the shelves is an example) -- although their customer service is mostly very very bad (some employees are very very good, but you have to be lucky to encounter one of those).
You can read more about the issues (and fixes) of 2.0.0 here:
https://www.mobileread.com/forums/sho...d.php?t=184373 but it's a looooong read