This game is actually pretty great so long as you let go of your expectations of what a tower defense should be.
There is no pause, but this is to emphasize the tension of racing to get towers built in time. It is kind of charming in an old-school way when you fail because you weren't fast enough.
The first night I played this I got frustrated around level 9, but after thinking about and going back to it the next day I beat the level solidly.
After beating the game, I even went back and beat all the levels on hard difficulty and without juggling. So the game doesn't require juggling to beat.
You MUST pay attention to what the towers are strong and weak againt. Having a good variety of towers and upgrading a tower to transform it to be strong against the next wave helps immensely.
For half-off or even 75% off as I've seen this game for now it is a good buy.