For any fans of WWI/II/Korea aviation there's a new game called War Thunder that's in open beta test right now available on Steam. It's free to download/play at the moment. Online play team vs team, wide variety of aircraft that is somewhat customizable, detailed damage, and multiple realism modes from 'arcade' to 'I've got windburn on my face' (aka "Historical"). I've been playing it for a couple of days now and am finding it pretty fun entertaining. (tip: unlike most war aviation sims, AA fire and flak are NOT just for show, much to my surprised chagrin.)
Will also be expanded to include playable ground and naval units in the future. It's also one of the few fighter sims that is easily played with a mouse and keyboard as well as console controllers or joysticks.