Hi. The main difference with the full version is that you have access to all the equipment, which gives you a much better chance of earning enough and surviving all five days as the weather gets dangerously cold.
It's true that this game hasn't grown anything like Real World Fly Fishing, but maybe that could change. Overall Ice Fishing Derby is designed to be more casual, more entertaining, and fun to the point of being addictive, but less of a serious simulation, so it would appeal to a wider range of people than just those who enjoy real ice fishing. On the other hand I've heard from several people who would like a game to give them more direct control over where to fish, how deep to fish, controlling the rod, reel and drag setting while playing a fish, etc. Perhaps the best approach would be to give the game two modes: casual (as it is now) and serious (more direct control.) Today the full version has only the one lake, but if we had a more serious ice fishing mode then it would certainly make sense to support multiple lakes, each with different habitats and fish populations. And if you can pick where to fish, it would make sense to let you drive a truck or snowmobile on the lake too.
That's starting to sound like a design for Ice Fishing Derby 2. The big question that brings up is: How many people would buy a serious ice fishing simulation? In other words, how much overlap is there between real ice anglers and gamers or potential gamers?