You might find very good can communities in so called "boring" games like IL-2 Sturmoviv because they charm an "older" fanbase and "ZOMFG GORE ANT TITZ !" kiddies stay away from serious WW2 flightsimulaters.
In the time I played AoM, I can remember that they had a great fanbase. Great gane too
Very fucked are most of the RTS fanbases, DoW is a collection of fucktards, just hang 30sec in the ingame channel and you will understand. Also, it wasnt a wise idea to allow the player to import their own banners and badges. So, you might find yourself playing between a team of porn and swastika banner using mongos.
Cant say any better about ZH, because there are abuseable cheats in the game, so its pretty much dead and destroyed, everyone is frustrated.
Supreme Commander has a good community, but it seems to me, they just split into vannila, fa fans and fa hater.
Guild Wars is a secret Nazi operation base, without having a kickass PvP rank you never get in any PvP party so they destroy the experiance for new players because if you arent member of the highlvl PvP master race, you are just unworthy scum and the fact that many players play like they traded their brain for bullcrap and run into every danger because there might be a monk in the party that can heal 7 dumpasses at once. If some one dies, its always the monks fault.