It's you
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I don't think this is an "insanely difficult" game, but for the average shooter fan I'd say Download provides a decent challenge. Download is not a walk in the park.
I know it will sound corny, but I suggest you experiment with different weapons to see which one works best for you (consider the enemies!).
How do you feel maneuvering the ship? Is the ship too sluggish, or is it about right?
There are many moments when things get crazy in the game (swirling graphics may induce vertigo!), and you have to concentrate and focus on shooting the enemies/bosses, despite the urge to get distracted by swirling madness.