The Colour Genie actually has a lot more games than it gets credit for. However, it doesn't have very many 'good' games. In fact, the best games for the Colour Genie would be largely considered mediocre on most other formats. I mean, I suppose they're better than playing on a 1K ZX81, but you get the point.
And so we have Jump Jack, a game which was released by Arcade Games (What an original name!) and which I had never heard of until it turned up in a bag of backup copies acquired via eBay. You load it with the SYSTEM command so you know it is at least written in machine code, but it starts with the title "ACRADE GAMES PRESENTS" which is a fairly early indication that what's coming up is going to be largely unpolished.
And so it indeed proves. Jump Jack is one of the most basic games I've ever seen. You get a screen of five scrolling lines and at the bottom of the screen you get Jack, a fairly good sprite (for the Genie) that can be moved left and right and can jump. The lines have a Jack-sized hole in them that needs to be brought parallel to Jack's head for the jump to successfully bring him another fifth of screen higher and if you get to the top you win. And get to do it again. Lucky you.
If you bash Jack's head in (much more entertaining) he falls back stunned and if you're unlucky he can be stunned for so long that he keeps falling through the holes in the lines until he's right back at the bottom of the screen. Each involuntary headbutt will cost you one of your three lives.
Sound is reasonable (again, for the Genie) with a little tune playing when Jack moves. But overall the presentation is very poor. Yes, it works and with a bit of skill you can master it. One game is going to be enough for anyone though. A great game to get for someone you really hate.