Isn't the script what made Collateral great? Originally it was a shitty action movie about a hitman named so cleverly "Mr. Collateral." Mann, along with others rewrote the script, Mann being the biggest influence on turning it into a great crime drama. The ending was probably the best way it could've ended, but the problem was the rising action, which almost took a Terminator turn.

I'd pick Simon West or Rob Cohen for my torture.