In a game so charming and so full of detail and craft, the alarmingly bad "Simlish" really stands out. It's over-processed and doesn't flow very nicely and the main characters (Cappy, the Broodals, Bowser, etc.) are probably the worst offenders.
It's the only thing in the game so far that misses the mark. I can practically hear the business meetings in my head whenever someone in the game speaks.