In my opinion, this canon puzzle is a nice introduction to sequential discovery puzzles.
Well, there are some controversial talks about what is a SD (sequential discovery) puzzle. In my opinion, it's when you have several steps to open the puzzle and at least one tool to find and use to solve another step. Maybe there should be an even more difference between SD puzzles in the way that you cannot compare a SD with only one tool and a SD with many tools / secrets / steps.
So I would tend to classify as following:
SD: puzzle with one tool to use and several steps
SD+: several steps and max 2 tools
SD+++: more than 2 tools and several steps
Now the difficulty would be to evaluate what is a tool and what is not, but that's another story.
So for this one it's a SD according to my classification, especially considering that it even suitable for beginners.
The goal of the puzzle is to find the cannon ball. What's nice with the puzzle is that it has a metal support, to try to look like a real cannon.
A not tool difficult but nonetheless nice puzzle that you should own and show to your guest (if they are not seasoned puzzlers!)