After two books of the Gabriel Allon series (one early, and one late in the series), I can say that Daniel Silva is one of my favorite authors of the Spy Thriller. Not as psychologically dense as Le Carre, but not soulless, Silva seems to have a good balance between the psychology of the character and the action of a thriller.
I felt The Kill Artist
was solid. The characters had dimension, and did not require a great effort of suspending disbelief, even looking at this through post-9/11 eyes. (Some disbelief must be set aside, but what the hell, it's fiction.) The plot was fun to follow and relevant for the time it was written (before Osama bin Laden changed the game).
If you like a spy thriller that is not shallow like Ian Fleming, does not become over-laden with the inner workings of the character like Le Carre, but still has the soul and psychology of what drives an espionage agent, then I recommend this book.