Tried again for Shards of God. Readme can't be opened as well. It is complaining about insufficient access rights. The game file says that the image is corrupted.
If it says something like "Shards_of_God_v1.2 is damaged and can't be opened. You should eject the disk image", then that's bs and a pretty sleazy move on Apple's part - the file isn't "damaged", it just doesn't have an app store license. I don't know why you can't open the readme though, that's strange - will ask the person who made the package and get back to you.