Creator Backlash: Daniel Craig wasn't fond of how production went (Reports suggest he and the director were making it up as they went along), saying that thanks to Quantum, he'd never do a film without a script nailed down again. (Fortunately, it didn't turn him off doing another Bond film, as it was followed by the far superior Skyfall.)
Troubled Production: The film was stalled in pre-production by a writers' strike. Based on various accounts, screenwriter Paul Haggis was frantically finishing a first draft hours before the strike deadline and/or Daniel Craig and director Marc Forster rewrote script pages themselves during production. In addition, the fragmented nature of the production (due to the strike) led to a rushed and nearly-incoherent plot.
The film wasn't originally a direct sequel to Casino Royale (2006), but seeing as the 2007 Writer's Strike left them with the minimum of a script it was given stronger connections to the preceding movie.
Al Pacino was reportedly considered for General Medrano.