We sat, we watched, we flung. To my regret, the litterbox was two floors away.
The writing seemed entirely bent on creating drama (and a love triangle) where very little existed (as one might expect from a movie) while overlooking parts of the real Ewan Montagu's account which would have added much - like a ring of truth. The corpse of the Welshman was frozen, so that Weekend at Bernie's photo shoot was ridiculous - their main problem, as they prepared him for transit (per my spouse) was getting his boots on over frozen feet. The typerration was indeed annoying, and odd coming from Fleming when it is Montagu's account of events that is the basis for most of what we know. Fleming did contribute to the Trout memo, but remained in Adm. Godfrey's office, and would have not been at a desk in the Group XX room.
What really failed was the extreme magnification of Montagu's romantic interest in Leslie, which seemed subtle as a buzzsaw wristwatch and too obvious an attempt to keep the film from being overly procedural by injection of Casablanca tropes. It rings false, and Firth's goyish looks would be ill-suited to the real Montagu's Jewish guilt.
The bit about Hitler's senior intelligence man in the Abwehr seemed to draw mainly from the historical fact that Von Roenne was later linked to comspirators in the Hitler assassination attempt, and was anti-Nazi party. The mystery man in Leslie's apartment, however, seems a weird speculative tack, and tossed in to add suspense. Given that most viewers of such a film are aware the Allies succeeded in their invasion, I'm not sure this kind of twist really adds much. It simply pulls the viewer out of the film enough to say, well, Mincemeat was swallowed, so this is nothing really.