This a well-written example of male wish fulfilment fantasy. I think this offers men an analogue of the escapism offered in bodice-ripper romances.
It gives us the chance to imagine being someone we know we'll never be and someone that, deep down, we know we don't want to be: a disciplined, potent, loner who has all the toys and all the money but is still driven by a code of honour to protect the weak.
It's a world where problems can be solved with violence and sacrifice. Where women need to be rescued and bad people need to be killed.
The hero pays a price, of course, or else he wouldn't be a hero. He's burdened with isolation, the constant risk of death or injury and the need to keep secret who he is.
Still, the opportunity to be Batman without the melodramatics of that creepy cape has a strong appeal.
The best part is, when I close the book, I can return to civilisation and the rule of law and frown upon any would-be vigilantes trying to impose Jack Bauer problem solving on the real world.