History lesson, or game?
This is kind of an anti-game. You seem to want to tell a story that has been endlessly re-told since D-day happened, so it makes the movie clips rather redudant to anyone who's heard about WW2. Maybe if you want to make a defender game, go ahead and choose the WW2 era, just skip the history book lessons or the "dramatic" voice acting.
On the game side of things, it was enjoyable and just hard enough to make you want to play. The power-ups felt like fringe benefits because they came so infrequently, but they were useful when they came around. Perhaps instead of randomizing the engineers' thing, let users choose; it'll add some more depth to the game.
6/10