I have several books on this topic but Jimenez's is the best. He writes very nicely and keeps you entertained and informed, I highly recommend this book, even if you have read other books on this topic.
Casear Against the Celts takes the reader on each of Caesar's campaigns in ancient France, Britain and Germany, describing his battles on land and sea, including the invasions of England, the bridge across the Rhine, and sieges of numerous Celtic strongholds.
I love history, but I must admit I didn't know too much about Julius Caesar. Learned an awful lot in this book! Well written, thoughtful, and full of goofy well researched details, much of it from Caesar's own writing.