IL-2 BOS and COD tend to be quick WW2 fixes for me. I can imagine that they would be both excellent for MP. The B/C Mustang and Mossie are incredibly beautiful and fun to fly. Never mind that the early Stang only has 4 x .50s. It can shred enemy fighters as you channel your inner Gentile and Godfrey. The Mossie is a beast that can hunt bombers as well as move serious mud. The way that you almost have to loft the rockets seems realistic, is a challenge, but huge fun when you get it right.
However, my most immersive single player experience by far is flying Reflected WW2 campaigns. The way that he forces you to fly the aircraft and communicate as historically correct as possible, adds so much to the experience. DCS, with all of its faults, still has superior radio and scripted voice ability over the IL-2 offerings, especially in the hands of a skilled mission designer.
Even though it’s one of his early campaigns, Blue Nosed Bastards, especially in VR, is the whole enchilada. I detailed some of its goodness in a short review with minimum spoilers. Note that you have to follow the script, cold & dark starts, taxi on time, join ups in position, make checkpoints, and be on the right frequency for success, but this makes it so much more immersive than diving into a furball, which you will have every now and then regardless.
Wolf Pack for the Thunderbolt is more of the same. More refined and depending on your skill set, perhaps more challenging. Really looking forward to the Reflected’s Mossie campaign.