It's not very frequent, but there are three moments for me.
One of them is flying through a formation of bombers, and I mean a GOOD formation, not one of those messy usual formations. When there a few talented pilots together, sometimes they make this beautiful bomber formation looking very historical, and flying near them and watching them move together like a big, fat herd of cows, is very exciting.
The second, is looking at planes take off in the mission. Likewise, not those messy take-offs where everybody jams full throttle the moment they spawn, but when a close groupd of pilots call out "roll 1".. "roll 2" and one by one, I see their planes up in front of me.. and when the moment comes where it's my turn to roll, that's a very immersive moment.

The third, is attacking a train with an IL-2. I almost never survive from that(those train acks are tough!), and seeing a train is pretty rare anyway.. but in those rare moments where I get to meet a train in an IL-2.. and as you approach the steam engine compartment and let the cannons rip.. that always brings out a smile on my face.