1 star = something seriously wrong
2 stars = meh
3 stars = a like of sorts (not a negative rating here)
4 stars = really enjoyed
5 stars = loved and/or a new favourite
1 star used to be reserved for books I didn't finish however I have started an un-rated DNF system. I rarely give out 1 star rating these days because life's too short to read bad books!
2 stars is an OK read but nothing special. Often it's the writing style that lands a book this rating. Or particularly annoying characters. Also used when there's more sex than plot! Before you dismiss these books, they are usually ones that I think some people would enjoy, they just weren't for me.
3 stars is not a bad rating, it's above average and often these are very enjoyable books. Sometimes they are great fun but not very well written or maybe or books that just didn't draw me in as much as I wanted. If you read my reviews you will get a better idea as there are so many reasons to give a book 3 stars (I would normally upgrade these to 4 stars on Amazon).
4 stars is a pretty good book. There's only a little something that's stopping it getting full marks. Too much talk of pregnancy or babies can cause this or some plot device that I generally don't like. All this means you could very well love the book. I also use this rating for books that I really enjoyed but know deep down that they're not that brilliant, just enjoyable at that moment in time to me!
5 stars does what it says on the tin. These books kept me up at night and would be the first thing on my mind in the morning. Sometimes a work of literary brilliance, sometimes amazing characters or unique plot.
DNF does not necessarily mean the book is bad, it's just for some reason I decided I didn't want to carry on. Some of these books have real potential and if you read my DNF posts you will find an explanation.