Want realism?
This style and strategy completely changes how to play and even why to play, and it makes the game difficult to play and fun to play too. The learning curve is shallow or steep depending on your aircraft, the strategy you need to defeat your enemy, and how to land your aircraft without hitting the ground too hard. Knowledge of how to fly, fight with and successfully land a small plane cannot be readily transferred to a bomber and vice versa. Taking off and making it to your target is no guarantee of success, no matter how skilled you are. One stray bullet to the body or head changes everything. If they knock out your engine, or it catches on fire, you stall your aircraft, or any of these results changes the game dramatically. Sure you can hit Escape and try again, but there is a certain kind of satisfaction at bringing you damaged plane (and body) to the ground and walking away when you are hurt that is rather appealing and realistic. There is more to the game than dog fights, you can take on any role in the aircraft and become a gunner instead of the pilot or be required to attack ground targets. Attacking ground targets without bombs is like trying to throw a coin 50 feet into an open window on the side of car on a windy day. You might get lucky, but more likely you're wasting your time. Equiping your aircraft with bombs on a mission involving a dog fight is like trying to run a marathon in knee deep water. It will slow you down and make you more of a target.
It's all these subtle complexities that makes IL-2 and the recent 1946 expansion very appealing and highly recommended game.
About the only thing I don't like about the game is the way in which it gives you points for kills. But that's such a minor point if you get killed, shot up and have to bail in mid-fight.