One of the more impressive things about the Echo is its far-field mic. I've used a lot of different voice recognition technologies, but Echo blows everything else away in terms of being able to speak in a normal voice from the other side of the room and have it still understand you. The actual intelligence behind the service may be lacking (or at least behind some of the competition), but for a general-purpose home a…
In my limited experience using Echo at my parents house over the holidays I was distinctly not impressed by the Echo's abilities to understand voice from across the room. We often had to repeat ourselves, only louder and slower to get the Echo to understand us. We do not have strong accents.
Many of the commands it "fails" at is when it tries to "guess" what I might have meant to say because it can't find something in its database. For example, if I give it a wrong name for a song (say "Alexa play She's Leaving by The Beatles" it might play some song called "She's Leaving" by some other band because it can't find that song under The Beatles.