I’d say it’s a lot of chopping wood. The difficulty is in lasting that long, compared to some games which have various objectives that are difficulty within their own right on top of the challenge of surviving that long. (Think Alien Invasion on TSPP)
And most of the shots are relatively safe if you’re willing to take your time and are more focused on getting to the end than racking up a massive score.
That said, I do love the game and it’s on my wishlist.