I actually listened to all but the last story, Triangle at Rhodes. Overall:
Murder in the Mews: This is a novella length Poirot story, which I listened to on a 2 hour drive that extended to 3 hours because of some traffic delays. It held my attention, and has an interesting twist at the end. The most interesting of the bunch, in my opinion.
The Incredible Theft: I usually find it a bit meh when Christie goes political (except for The Secret of Chimneys. I love that one). This was no exception. I figured out the solution to this one pretty easily, and didn't think much of any of the characters.
Dead Man's Mirror: This is the most classically Poirot of the four stories in this book. It is quite a long story, and well-developed. The victim in this case, Gervase Chevenix-Gore was an interesting and unlikeable fellow.
Triangle at Rhodes: Started out like Evil Under the Sun, ended up like Death on the Nile. Quite short. Well done.
I am not a huge fan of short stories, and these were no exception, however. I much prefer my narratives novel-length.