I rate primarily on an emotional level and not on a technical one. A book could be beautifully written, but if I didn’t enjoy it, it won’t get a high rating from me. 3-5 stars is considered a ‘good’ rating.
DNF - did not finish - you won’t see this from me much because even if I’m not enjoying a book, I tend to skim to the end enough to know the story, in which case you’ll likely see a 1 or 1.5 rating.
1 Star - really didn’t like.
1.5 Stars – didn’t enjoy it.
2 Stars - not for me/didn’t like.
2.5 Stars - okay but not really for me. Check the library.
3 Stars - okay, liked it. Maybe check the library first.
3.5 Stars – good. Worth reading and probably owning.
4 Stars – great! Buy it.
4.5 Stars - loved it! Really awesome read and you need to own it!!
5 Stars - perfect read!! Buy it. Right. Now. That is an order. :) Full marks is something I've given out fairly freely in the past, but as of 2011, this is going to be reserved for those books that have that little something extra. So you can consider 4.5 stars pretty much full marks from me!