Pretty cool app! The Letters game was great, but I felt a bit pressed for time in the others - I know that's the aim of the game, but if you make a mistake, you have very little time to make up for it.
What other mini games are you planning? Hopefully some kind of word puzzles, like 'Unscramble the Word' or 'Missing letters'. Maybe a maze too?
Other than that, the game plays very well. It responds quickly to inputs, but you may want make the detection/hit boxes larger on the Letters game.
Reminds me of Crash Ball in Crash Bash (PS1) - which is a good thing; it's mad fun if you've ever played it - where you protect your goal with ship capable strafing left and right.
The added challenge of the kick, magnets and other players made for some pretty hectic gameplay. Not saying you should copy the idea, but perhaps use it as inspiration for additional soul powers and stuff. This video, however, doesn't quite show how fast-paced the action is, but shows the different abilities.
That said, the fast-paced nature of Crash Ball was probably the most exciting thing. Whilst a lot is going on in your video, it might be worth a look in making the level a bit bigger and making everything move a bit faster.
Certainly like the repulsor fields, the expanding sheild surface and the turret.