It's impressive that you wrote your own engine in the span of the game jam. For Chain Reaction itself, the use of procedural generation is interesting, especially for the music. Unfortunately, it ended up making the final game too luck-based; I was able to get close to 80% of the orbs destroyed sometimes, but other times, I'd get under 20%. A game based around this concept, but with pre-made levels and other gimmicks added, could be fun, and I'd encourage you to keep going with it. I don't know too much about the Atari 7800, but aside from a few of the transparency effects, this feels like an Atari game. Finally, the Minesweeper and Snooker games were nice extras to demonstrate the capabilities of your engine.