9. Ace Combat
I'll admit that this isn't a series that is well-known by many gamers, but I've snuck it on here as it's a personal favourite of mine. Flight sims don't usually get noticed that much, but Namco and Project Aces pulled out all of the stops when they released Assault Horizon. The game was a commercial success, selling over a million companies, which only strengthens the argument for another sequel in a series which has been around since 1992 and features 12 games. Things have been rather quiet though since the 2011 release, and with a 2013 release scheduled for PC, it seems that the developers are rather busy. Still, there definitely will be a sequel some day so here's hoping that it will be this year.