It's probably the simplest puzzle game there can be while still offering some challenge. There's a limited amount of things you can do with this idea, but I'd say that the last two levels were something that required a bit of thinking before just going for it. The rewind feature is very useful in this case. I'd say that 289 kb is impressively little for an actual game, I remember that the memory cards for the original PlayStation held 1 megabyte, you could fit easily three copies of this in there!
If you're interested, you'd be welcome to enter our Game Development World Championship!