Okay, some more info has come to light re the "bland" characters seen in the L4D2 trailers. (Doubters, prepare to be humbled.) They are: Coach, Ellis, Nick and Rochelle; the collected members of the Church of Christ's Almighty Love That Rains from on High Like Blessed Lead, a militant evangelical sect of Christianity that practices polyandry (one woman may have several husbands), compulsory abortions (to keep more sin from entering the world) and mass shootings.
After returning from a wilderness retreat, held at their fortified compound in Texas, the quartet discover that the Apocalypse has come into effect a few days ahead of schedule. It is their God-given task to put down all the sinners of the world once and for all, starting with the wicked folk of New Orleans (did they not get the hint after that whole flood deal?!).
Each member of the group has a rich history, involving various childhood traumas, broken marriages and failed careers. Nick is a former sportswriter and NFL commentator who became a heroin addict after his wife and infant child were killed by the Washington Sniper; Coach is a "reformed" homosexual who used to work as a male model and fashion designer; Rochelle is a Pulitzer Prize-winning composer who denounced music as "blasphemous" and staged a public burning of the Well Tempered Klavier; and Ellis is a train driver from LA who lost his job when he developed epilepsy.