Great game, look and feel matches gameplay, didn't notice any bugs.
Some ideas:
1. power-ups should stay between levels until they are depleted or you die.
2. add a power-up to slow time for the enemies but not yourself in later levels.
3. Add a remote server/cloud based high-score table where you can enter your name and compare it to other real players.
4. More incentives to save your friends , maybe an extra life after collecting a few of them? didn't notice if this was already the case.