Just looks like someone forgot to screw the plastic front plate back on. This really isn't all that dangerous. Yes, it's far from ideal, but one would really need to work hard to get into a position whereby this could cause any sort of issue.
I'm frankly stunned that the hotel comped your night. Wow. We can all agree that someone should've replaced the electrical plate, but I would simply have let the front desk know the next morning that maintenance should go do so -- it wouldn't have occured to me to make this into an "issue" of any consequence