For me it the immersion mostly and sometimes the kick-in-an-armchair.
For the immersion of the feeling how it could have been, that you can forget about real life for a time in a thrilling way, especially if you are fond of aviation and history. For that part I preferred singleplayer because you simply had no online play available providing historical schemes and player which act accordingly. In single player you have the numbers of planes flying formation, doing their assigned task and you are just one of many trying to contribute to your given task and survive. It is up to you how you engage into a combat, plan a sortie, keep station in the formation and play your role. Sometimes 1946 online play was close to that in on-line wars as AFW or VOW. That`s on what I orientated our squad server, you have one life, one task, limited resources and have to cooperate with your team to achieve your objective. Even though your team-mates might be AI it is more immersive to fly in a wing of AI with coordinated opposition. At least the AI cooperates better as the standard online player and do go for the objective (well, in most cases). There is nothing more immersion killing than meeting a solitary fighter flying around looking for something to shoot at. That`s when I am looking for immersion.
On the other side there is the kick in your armchair also as a pure matter of entertainment. That`s when you fly around on the standard dogfight server without any purpose just looking for trouble and some casual enemy fighter or bomber flying around on the classical dogfight server. Then still the heartbeat gets faster if get into an intense twist, with a knife between your teeth. It is the total opposite of the immersion, but it`s fun too and I still remember my first online fight, which I noticed as a fight, in which I was so nervous and excited that I could hardly hold the joystick, not to speak of aiming. That excitement has settled widely but is still there for some extend, even after all the years.
