CURSOR Magazine published some very good programs on cassette for the Karma. Two that come to mind were RATRUN, a 3D "rat maze" in which you had to find the cheese, and Indian Poker. In the latter, you could see your opponent's cards, but not your own, and had to try to win bets. What made it special was that each opponent had a unique "personality". You could sometimes tell from their expression whether they were trying to bluff you. I found it amazing that anyone could squeeze such impressive games into 8KB of memory. Try to find anything that will run in 8MB today. :-)
I fried my brother's by inserting a cartridge while the machine was powered on. I think I had to pay $75 to replace the CPU (and maybe the entire motherboard). Afterwards I looked at the schematics and found out why I fried it - The cartridge was unbuffered. If you put it in even slightly skewed, it would short out several lines in the computer.