Combat flight simulators

H.A.W.X. is a relatively recent combat flight simulator with decent reviews.

Out of curiosity, can you give me any numbers?

TheViper, H.A.W.X. looks rather arcadish.

Doesn't look bad.
Though, lot of people are complaining about the lack of planes (CC if you want more) and that you have to be constantly online even when playing in single player mode.

You also might get some help about number of active players here:

http://forums.ubi.com/eve/forums/a/frm/f/23110283

I am currently playing IL2 online on a casual basis a few hours each weekend. I am well past my best however in the world of combat flight sims and the online version of the game is very unforgiving to newcomers. There are a lot of very hardcore players online that have been playing the game for many years and who like to make very short work of new players. A lot of them use teamspeak for communication purposes and so unless you have that set up I expect you miss out on a lot of the in-game communication.

If you want to give it a go, you'll need IL2-1946 patched according to whatever server it is you want to play on (v4.08 is the basic patch and most widely accepted).
The best way to connect to an online game is the 'hyperlobby' software (as mentioned in a previous post above) that you need to download and install as a separate program (if you haven't already done so). The game is still very popular and you may struggle to connect to some of the more popular servers, depending on the time of day.

Apparently there is a new game from the same developer due to be released next year, 'battle of britain storm of war' which, as the title of the game would suggest, is focussed on the battle of britain, though I suspect it might cover up to 1942.