There are times when Holmes and Watson seem just a bit out of place in the World War II setting, but "Sherlock Holmes and the Secret Weapon" still has enough of the Holmes flavor to be worth watching. It's mostly enjoyable, with Holmes's usual deductions, disguises, and the like making up for the occasional war-time messages that come in from time-to-time. There are also some good moments of suspense, plus some pleasantly offbeat plot details, to keep your attention.
The plot gets pretty involved, with Holmes involved in protecting an inventor whose ideas the Nazis would like to get hold of. Some good turns follow as everything is played out in an interesting battle of wits. The supporting cast includes Lionell Atwill and Dennis Hoey, who are solid as Moriarty and Lestrade, respectively, plus Kaaren Verne.
Overall, most fans of the Rathbone/Bruce series should find it an enjoyable feature.