I use a five star rating system similar to Goodreads, but here's my definition of what the stars mean.
5 stars- Highly recommend this book. It's well written, love the storyline and characters.
4 stars- I still really love this book. There are a few problems I have with the book, which are addressed within the review, but I still recommend these books and love them.
3 stars- This is where the reviews depend on each book. I've had 3 star books I've really enjoyed and love as an introduction to a series or as a book by itself, and there are 3 star books that I was really let down by some aspects of the book, but it also has very strong points as well.
2 stars- I probably didn't enjoy this book very much. It was decent, and I finished it, but I won't reread it and probably wouldn't recommend it.
1 star- I had serious issues with this book. In some cases, I can't get through 1 star books.
In general, these are my guidelines for how to interpret my reviews. However, these are all based on my opinion, and there are always varied responses to books. I would encourage you to read a book if you are interested in it, and then discuss it as well.