I've been able to spend a few weeks lovingly and obsessively creating Miis that represent me, my family and Robotech characters. It's a blast, but I have a few suggestions:
1) Picking a gender for your Mii shouldn't be mandatory. I understand why its there-- we're always asked what our gender is, from surveys to signing up for MSN Messenger. The Mii Channel uses it so that when a gender is chosen the haircuts that show up first correspond with whatever gender you chose. But what if you want to create an androgynous Mii (which is surprisingly easy to do) and you don't want to identify the Mii as male or female? It's unnecessary.
2) Haircuts should be organized by length instead of gender. Other categories, such as lips and eyes aren’t separated, so why is hair length? There aren't any restrictions in regards to choosing a feminine haircut for a male Mii anyway (which is awesome), so the distinction seems arbitrary. Having the hairstyles grouped by length would make customizing easier.
3) There should be more control over body type. I keep on running into this problem—I wanted to give the Mii that's supposed to look like me some hips, but I couldn't. Similarly, when I was trying to make an animorphic representation of my overweight cat, I couldn't make him look fat enough. Rats.
4) Untraditional hair colors need to be included. I know I'm not the only one out there who likes pink hair. And what about making a Mii that looks like Max Sterling? Only blue will do. Actually, a whole color wheel or spectrum should be included so that there are more hues for skin color and more choices for the color of clothing.
I'm thinking that a lot these issues could be remedied by an update. So what do you say, Nintendo?