Cliffs of Dover is a dog of a game. While beautiful, it's extremely poorly optimized. There's absolutely no reason it should run as poorly as it does.
Moreover there is no Dynamic Campaign which is something that made the original IL2-Sturmovik a great game. Also add to that there are only about a dozen flyable planes, most of that dozen taken up by various variants of the same aircraft. Compare that to 229 flyable aircraft in the original game. Sure that comes with the expansions, but still...
There's also tons of bugs, really stupid AI, and completely unintelligible voice acting.
With the original game being only $10 on Steam with all of it's expansions it's an infinitely better value, better sim, and more fun experience than Cliffs of Dover. Wait till it's in the budget bin.