Most importantly, it also allows you to see whether or not your game is even fun to play. One of the worst things you could do is finish your game only to realize that absolutely no one else likes it, or even worse YOU don't even like it. If that is the case, and you have discovered part way through development that your game isn't fun, what do you do?
Do you start from scratch? I wouldn't say starting completely from scratch is a good idea, unless the basic concept of the game doesn't make sense, or if there is absolutely nothing that can be salvaged from your game. In that case, you may not have a choice.
Do you start adding things to see if it is fun? No. Adding things to make it fun is going to lead you down a long road of disappointment. Your game needs to be fun at its core, not at the tacky addons that you tossed in there to zazz it up. Adding things in to make it fun will only drain you of your time and money, and in the end you will probably end up in the exact same position you started with.
Do you abandon all hopes? Never, unless you would rather change hobbies/jobs and become the cat food specialist you always dreamed of.
Recently at LoneWolfPack Interactive, we came across this exact issue with our current project, formerly known as Sudoku Rush. The other day we were playing the game, talked with each other, and decided that we needed a complete redesign. There was absolutely nothing redeeming about our current idea, and we needed to overhaul the entire game.
Sudoku Rush was our take on the action puzzle genre. We wanted to make Sudoku more exciting by adding a base defence element to it, which sounded like a good idea at the time. Unfortunately, it didn't turn out that way.
There were good things about it though. Since Sudoku has been gaining popularity over the years, having Sudoku attached to the game would have made it come up on search results fairly often on the store, so it would have gotten easy exposure. It was also very different, and since the market is getting saturated with very similar titles, it was nice to see and to work on something new. It was also an easy concept to get the hang of. Filling in the Sudoku board gave you money that you could use to spawn units.
There were a lot of large problems with it. For one, the game just wasn't fun at all. There was no 'this is it' moment, where we knew we had something good. There wasn't enough player control, if you sucked at Sudoku, you stood no chance, and if you had enemies right at your base you needed to solve a ton of numbers on the puzzle to spawn units. In general the game was overwhelming as well. Solving Sudoku puzzles, spawning units and controlling them, and keeping track of what was on the field was just too much for the player. Finally there was no real direction for the game.
So seeing all of the issues, we decided to come up with a completely different direction for the game. We stripped Sudoku right out of the game, and changed how the base defence works. Since we wanted to give the player more control during the game, we decided to give the player hero units to control. With this set up there is a lot more action, and having hero characters provides another avenue for future content. The game is also set up in a similar fashion to games like League of Legends or AirMech, so there is that appeal as well.
We are excited with the new idea, and it will definitely be more fun and more appealing to players. There are a few new small problems, but they are much more manageable, and they are not problems with design, but they are just problems with changing the game at the last minute. The scope of the game is much larger than the old version. Giving the player more control over the hero units, allowing the player to upgrade these units and keeping everything balanced is going to be much more work. On top of that the AI needs a lot of work. The AI needs to transition from figuring out which units to spawn to controlling it's own hero unit and doing things intelligently. It will be interesting to implement.
Overall though, we are happy with the new direction. It will be much more fun to play and to build, and it shows you that you shouldn't be afraid to try new things, even after you've invested time into them.