I think there are two reasonable things that need to occur for this to be a 3 star time waster:
1. Aim needs to be consistent. You can swipe in the same place, in the same way, but produce projectiles going in three different directions.
2. Hit enemies at point blank range. Related to #1, if an enemy is right in front of you, and you have no way to actually attack that enemy without frustratingly swiping at the screen like a confused monkey, that's a massive issue.
You'll notice both of my problems are related to aiming. Why? Because it is (quite literally) the only playable interaction you have with the game. You had one job, and you failed.
One star for not figuring out a mechanic that has been mastered on the iOS for nearly 10 years now.