I did Edexcel for Chemistry so I don't know what the textbooks are like for AQA, but the Edexcel one i was given wasn't that good. A textbook on its own is definitely not enough for an A* on it's own though. For chemistry I recommend chemguide.com for very good explanations, and the person who created the site also has a very good textbook on calculations called 'Calculations in AS/A level Chemistry' for both AS and A2.