I just accidentally purchased plants vs zombies for my kids on he 360, accidentally because I didn't realize it was EA. micro transactions all over the place, cant play unless you sign up for Origin and everyone's mic is on with no option to turn it off globally, have to manually mute everyone when the game starts. Deleted!
I was looking for a way to introduce coding concepts to my kids but this title ended up being less intuitive than teaching them from a text editor. This game has a good amount of free drag&drop props and playable characters but it seems to be directing you toward in game purchases from the marketplace. The problem I see with paying for more usable content is you cannot do much with your finished project. If you take a lot of time and create a rich game in Spark, say spending significant money on new prop objects and characters, you have no chance to reclaim your investment. Hopefully some of what you learn while playing Project Spark will be transferable to real game design. If you want to make video games I would say the learning curve for Project Spark is about equal to that of most free game engines available on PC/MAC. If you have a personal computer I would recommend looking into Unity3d instead. Purchases made from their marketplace are yours to use in your own sell-able games. Even if you are making a free game just for fun, you will still be able to share it with more folks than those who play Project Spark.