Normally, I get antsy when I have to watch Cary Grant being frantic and flustered (like in Bringing Up Baby). I much prefer him when he's suave and in-control (like in His Girl Friday). But even though a lot of this movie is composed of him being pop-eyed and shooting goofy looks at the camera, I still enjoy it a lot.
For one thing, he's got good reason to be freaking out. The stakes get raised frequently and crazy things continue to happen. For another, the crazy things are themselves entertaining. It's Peter Lorre again! And I think he actually gets away clean, which is always nice.
Also, I think the aunts are great. I know it's an easy gag to have nice old ladies cheerfully talking about killing people, but they're really good at it!