I used to be a huge Lego fan, and have just recently heard about the minifigures. Luckily I got to a shop that still had series 1 and 2 and they were happy for me to sift out the ones I wanted so I bought up 3 sets.
I think the minifigures are fantastic - to me they are a celebration of human history, as well as Lego history with traditional figures like policeman/nurse/spaceman importantly included. It's amazing really that the minifigure design of 1978 has stayed so long and is even more widely recognised through new moulds/faces/accessories and computer games and animation.
I think they are missing musicians even though they have rapper and punk rocker they could go for more traditional - a female violinist or a female saxophonist would be great.
Because they have spaceman/cop/nurse I also think they should have definitely have a pirate with a hook if they can vary it/improve it from the figures that came with the pirate sets. And also a knight to celebrate the castle theme and the famous yellow castle set 375 which was either out in 1978 or 79.
The ultimate figure for me though if they could somehow do it is: -
Gender: Male
Occupation: Bagpipe Player
Type of Headgear: Scottish tammy hat
Type of Facial Expression: tired/strained/cheeks puffed out
Color: Tartan - predominantly green, blue, or red
Accessory: Bagpipes that could fit across both hands and to the mouth!
One other thing - I hope Lego don't go to overkill - I know there's so many possibilities for figures but 6 series to me should be the absolute limit and I would have preferred a bigger gap between each series.