Jandy Hardesty’s review published on Letterboxd:
This is kind of a goofy movie, which seems to be rather a common factor of late Wilder films. It has an opera sequence that results in Holmes being propositioned to be the father of a retiring singer's desired progeny, to which he insinuates that he and Watson are lovers. It has a damsel in distress who may just be a femme fatale. It has the Loch Ness Monster and a top secret government plot led by none other than Mycroft Holmes, Sherlock Holmes' smarter brother. It has circus midgets, murder and monks. It has Queen Victoria and decrepit Scottish castles. It has the kitchen sink, basically.
Not all this stuff necessarily works together, but it's the kind of escalation that made me constantly go "okay, so now THIS is happening," cracking an incredulous smile, and then going along for the ride. It's wildly uneven, but what can I say? It was fun.
And that opera scene is pretty awesome/incredible/hilarious/WTF.