To be honest, Smash bringing in the Miis just reminds me that Nintendo really need to update them.
There's a ton of characters you can't make because of limited hair-styles and the like but also a lot of the mii-using games don't seem to take into account how much people have to 'abuse' the system to make the more interesting Miis. What this means is when you meet them at your streetpass gate their face just breaks completely when they suddenly have anything other than a Neutral expression
As a simple example, my Mii doesn't look too crazy but in order to get a nice highlight on her eyes I had to use eyebrows, also the eyes I used look horrific unless you rotate them on their side: this means when she 'emotes' it can look pretty odd. On the more complex side, I dread to think what the awesome Ironman Mii I made would look like if he ever emoted :s