I've been playing casually for about a month - I say casually as I've been trying to take it slow and steady, learning some roles, champions, item sets, mechanics etc. Mostly been playing in Coop vs AI games and custom games to get used to the mechanics and rotations and find what I like to play with some PVP. My aim is to get better and not lol around - I am level 25 with what I feel is a good pool of champions. I've tended to stay away from click to move games before now, so that was a hurdle for me.
Anyway, I'm rambling...
I'm interested to see which roles you feel are underplayed. My guess is support, as support and healer roles tend to be underplayed in most online games. If there is an underplayed role, I might be tempted to fill and main it if it is a role I get on with.