Those were some very fun and clever puzzles! I liked all the different ways you had to use gravity with opposite-polarity blocks to transport your characters where you need to go. It created a fun feeling of instability and tension as you prepare to leap off towards the key. Level 12 was my favorite. It required good understanding of how to use the four players to work as platforms for each other. 

Here were my main gripes:

• All the levels after level 12 (except maybe the final level) are super easy. With levels 14 and 15, I just kept flipping gravity until the key fell where it needed to go.
• The push physics feel very clunky. You can't just tap the right arrow to inch the block a bit at a time since the block won't move at all until you've built a bit of speed. Then once it starts to move, it accelerates very quickly, requiring fast reaction time to cut off your movement before you push the block too hard and overshoot wherever you're trying to push it to.
• Level 7 was extremely tedious. Slowly stacking all those blocks without missing one took me many tries due to the wonky push physics constantly causing me to overshoot the pile (which I can't see because it's off the screen). Then when I finally stacked them all, I ended up doing this:

It happened to me twice, actually. There is no reason that level couldn't have had just three blocks.

But those issues aside, this was a thoroughly enjoyable puzzle game. Great work!