This is going to be a great game. If they follow the payday model they will keep adding and improving the game for a few years. They'll also add paid and free dlc and friends can play the dlc as long as one person owns it.
Payday has a huge cult following on steam, but the games have never had huge marketing /advertising. TWD title is going to bring a lot of new players who have never played an overkill game before. This game is going to be brutally hard. More difficult than a lot of casual gamers/AAA title gamers are use to. There will be some stealth missions, but overkill doesn't let you off the hook everytime. It's going to make L4D seem like a cake walk by comparison.