Actively playing games will eat up battery pretty quickly, and some games will run some processes in the background, which will also eat up battery. I don't have any personal experience with that particular app to compare battery usage, but the first thing I'm wondering is - how much time did you spend actively playing the game, and how far was the battery run down when it was at 40% usage? Because if the battery went from 100% to 90%, and 40% of that was this app, that's pretty easy to do playing for a little while. If you played it ten minutes and the battery went from 100% to 20%, and 40% of that usage was this app, that seems pretty bad, and suggests there is an issue with the app. (Which would then beg the question whether it's a bug, or whether the app is doing questionable things in the background.)