Hello there. I'm Jester, fellow Walfaser. I have many to say for your video.
First off, the bubbles. You can adjust the size and text placement by pressing the M key and click the bubble. T is for text placement, white S for bubble size, red S for bubble and text size, R for rotate, and P for bubble position. Experiment with it, you'll get the hang of it.
Next, the scene transitions. The scenes moving erratically is a bit annoying. You could improve it by using a screen capture software. Or if you can't do it, try using photoshop and experiment with layers and opacity, such as the previous scene and the next scene will be in the exact same position.
By the way, you could press the spacebar to enter theatre mode, which removes all the interface and you can use left and right keys to navigate between scenes. You can leave theatre mode by pressing the spacebar again.
I don't have anything to say much about the voice acting other than it's way too low.
Hope these things will help you improve. Happy Walfasing.