I like the idea, but the realization isn't very good. Should have started with a single turret and less bullets, then increase the difficulty from here on. Maybe with moving turrets, faster and slower bullets, exploding bullets, etc.
But less turrets. Less than 4 for sure, because this way you're just forced to focus on avoiding bullets and don't really have time to try to direct your shield towards the turrets.
I completed the first 2 levels, then gave up, as it felt too random. 3/5.