Heh, a lot of wild opinions about WW2OL here
I shall throw mine in therefore as well:
Currently WW2OL is the only sim that gives me the immersion of real war and real flying. Sure, the FM in flight sim side lacks some things that I am used to in AH/WB but the general physics, weapons modeling and simply the challenge of flying are quite superior.
I don't need dozens of different plane types to find the flying enjoyable. Being part of a huge war, which is raging on air and ground, sometimes at sea as well, more than balances the thing.
The combat simulator, ground and air war, with organized units conducting warfare, is amazing.
The Finnish ground unit, Osasto Lagus, with the Finnish air unit Kuhlmey and my squadron as the fighter detachment gives amazing pleasure in cooperative operations. Ground units give targets and yell for air support, our Stukas loiter and attack sighted enemy units or bases, fighters sweep skies and patrol to keep battle area clear for ground attack aircraft to do their magic. It's awesome, just unbelievable.
And when I get bored with flying I can hop to infantry or armor.
It's the combination of the various things, the great physics and feeling of being there, realism and immersion, that have made WW2OL the finest of the simulators for me. But I also keep accounts open in other sims and play them to keep myself up to date on them and enjoy what is happening there as well.