Since first reading The Firm I have been a fan of Grisham's. The Summons does hold your interest and keeps you wondering how it will end.
With that said, when I reached the end of the book it left me wanting more. Not because it was good, but because it left holes open in what I felt Grisham could have closed up. Overall, the book is a good read but the ending is less than satisfactory in my opinion.