1. add more text to the page, put a paragraph or two below the puzzle describing what it is. Use Keywords in that paragraph that you want ads for. You don't have to overdo the keyword usage, just sprinkle them in a few times.
2. Move the ads towards the center, closer to the puzzle. I wouldn't have even glanced at those ads on my widescreen if I wasn't looking for them. This will help your clickthrough rate.
3. Don't expect to get rich off adsense puzzle ads.
I agree that adding a little more text about the kind of ads you want would help, then also use google adsense targeting. This way google will use only the text that you think will help bring up relevant ads for your site. You might also consider having an about page that beside talking about the game discusses similar games and links to them. I have found having a few pages with similar content helps google when targeting ads.
"In order to properly implement this feature, you'll need to include a significant amount of content within the section targeting tags. Including insufficient content may result in less relevant ads or PSAs."
So you can't just surround the word "puzzle" for example with section targeting.
Have a link that exposes a text description of the puzzle called "Text Description of this Puzzle" or somesuch. If you use CSS to hide the div, Google will index it. This technically is considered cloaking, of course.
2. Move the ads towards the center, closer to the puzzle. I wouldn't have even glanced at those ads on my widescreen if I wasn't looking for them. This will help your clickthrough rate.
3. Don't expect to get rich off adsense puzzle ads.