I've really liked this series but Gravity was my least favourite. 
 I don't want to have to hide this because of spoilers and there are A LOT of spoilers if I start on about the things that reduced my enjoyment. I will say though that the book was really good at bringing my heart rate up and my emotions out. For that reason I liked the book. 
 I'm not sure I'll read the next one though. This one sort of wrapped it up for me I think.