How others will see it. This is a fim with obvious appeal for classic movie fans. The stars (Laughton, Dietrich, and Power) are past their prime, but retain their charm. Henry Daniell, Elsa Lanchester, and Una O'Connor are well regarded supporting players. Wilder and Christie provide further famous names.
The source material is so well known that Wilder, in order to actually make the ending a surprise, had to add two additional twists on top of the one in the source novel. These additional twists, predictably, aren't satisfying (more on this later) but still won't disappoint fans.
Add the drama of a murder trial, and some hammy acting on the part of our leads, and the classic film fan is almost certain to be delighted. "Modern" channel surfers will likely pass, put off by the black and white cinematography, the old-fashioned British dialogue and sets, and the absence of eye candy such as hottie girls and preposterous action sequences. Let them watch something else suitable to their level of maturity.
How I felt about it. Although Laughton is third-billed, he is the real star of the movie. He plays a Churchill-like character; knighted, blunt-spoken, and frail, but highly educated, respected, and intelligent. His heart problems have him managed like a child by a demanding nurse (real-life wife Lanchester). Laughton furthers the grown child role by being naughty: sneaking cigars and brandy, and accepting a stimulating murder case instead of putting up with lukewarm baths and scheduled naps in Bermuda shorts. Naughty Laughton also batters his keepers with a series of insults, sure to amuse an audience with sufficient patience to relish dry English wit.
Perhaps Laughton overdoes it a bit, and his monocle light show was tiresome even before the tries it on Dietrich. Laughton's performance is subtle, however, compared with Power, whose ridiculous courtroom theatrics would never be tolerated by a judge outside of a movie set. The biggest eye-roller comes when Power, confronted with letters confirming her guilt, implores his bigamous, cheating, (and middle-aged) wife, "Christine, tell him that you didn't write it! I know you didn't!" You are found guilty of hammy acting, and your divine punishment is to die of a heart attack before you can make another movie.
But can't it be excused if it's all theater? The husband and wife playing roles opposite to their true characters? No, since the most preposterous events are yet to come. I won't "spoil" you by revealing the final two plot twists, which come on top of the one you probably already know. But I will note that these twists are exaggerated by the production code then in place, which ensured that no foul deed goes unpunished. The real mystery here is why Dietrich, who plays such a cold customer, would do such things for (or against) her husband.