I had no game file in the one I downloaded and I think rar should work for me, I don't have to deep of a knowledge but I remember that it should have worked the last time.
Make sure you right click the rar file and then click extract all, and after extracting open the folder and double click BangMon.html and it should automatically open/launch the game in your browser
I don't know what it means if the file is empty, maybe extraction isn't working, or you might need to download the game again, the rar file is about 167 mb in size