Since it seems to be going around lately, here's a brief rundown of what my star ratings mean.
* - I almost never give a book one star. This is generally reserved for books where a lack of effort feels clear in the work, or a DNF which is so rife with problems that I cannot recommending it to anyone in good conscience. Very few books are that bad, to me.
** - I didn't like it. I feel a 2-star book has major flaws which had a huge impact on my enjoyment of the story, and which would severely limit who I could recommend the book to.
*** - If I like a book, if I enjoyed it, I'll generally give it at least this rating, but a book with 3 stars has some notable flaws. They just weren't enough, for me, to prevent my enjoyment. Also at 3 stars are books which I find to be technically well-written, but which I did not enjoy because of their execution.
**** - A book I enjoyed unabashedly and would probably recommend to other people on a general basis, instead of a based-on-specific-tastes basis, gets four stars. They have to be fun, with solid plotting, quality writing and enjoyable characters. Also, incredibly well-written books which I neither enjoyed or disliked.
***** - This is for the very best books - the enjoyable AND well written ones based on their genre and aims (so, a well-written all-ages superhero comic would probably cause fans of five-star lit-fic to turn up their noses. But I feel you have to take into account the aim of the work, in some quantity). And also, very rarely, it's for a book I enjoyed so wholly that I just can't seem to see or care about the flaws.