My main gripe with BF2/FH2 flying is the awfully short visibility, it's like flying in a fog all the time. Of course, this is more of an engine limitation, because otherwise you would see all across the small map, leaving nowehere to hide, and the engine would probably choke on itself. However, the visibility also limits tactical choices: you can't climb too high unless you want to lose the sight of the enemies (or hit the "glass ceiling" even if you're a male).
The second is the flight model itself, again I suspect this is more of an engine limitation. I wouldn't say it resembles a "jet" or "prop", it is its own thing that has very little to do with real physics (cf. ground vehicles and their ridiculously high-set centre of gravity). Yes, I realize a FPS shooter cannot have Falcon 4.0 style realism, but even many "flyer shooters" like Ace Combat 6 have a better flight model. Going back to the ancient Their Finest Hour that turns 28 this year, that had already a better WW2 flight model and despite being labeled as "simulator" at the time, would not be too difficult to learn if applied to a today's FPS (a stark reminder on just how primitive the games of those ancient times were). Nevermind that I'm spoiled rotten by the IL-2 series, which even at its easiest settings (which I rarely used after getting a "feel" of the more realistic flying) feels more like real flying (and again, those "easy" settings would not be too difficult to learn in a FPS, it's the "realistic" mode that takes real practice). Also, since the BF2 flight model is its own thing, the more experience you have of "real" flight games (in my case, 27 years, starting with Project: Stealth Fighter on the C64) the more you have to unlearn (like throttle that seems to have two settings only even when using a flightstick: war emergency power and idle, and when you start to lose speed, it happens so fast you will never recover from a stall or have time to increase power).
Yet, as an aviation enthusiast, I cannot resist trying flying every now and then, but time after time, I cannot bring myself spending the hours necessary to master the BF2 flight model.
Nevertheless, flying in FH2 is still fun every once in a while, even for a whole evening when there's a special event, and at its best, the chaos on Battle of Britain or Bombing the Reich maps is epic. But "pure" flying is not FH2's main forte, that would be the combined arms approach that meets the right amount of realism in ground combat.