It's an okay game. Art is great, and it doesn't even chug when I blast it at 2x speed. However, up until the 14th level all I did was spam ranged units, and then green blobs and it was an easy win every time.
The 14th round at the very start of where enemies come, you place a blob, little armored dude, diamond stunning thing, blob, armored dude, diamond, then the rest the blue square slow guys. It took a long time for me to realize the armored guys are VERY weak but once upgraded, they upgrade in speed and damage significantly. Upgrade all those on the bottom floor to max (except the blue square dudes) and line the 2nd floor with the rectangle blocks that shoot above and below floors. This strategy also works for the 15th and last level - nothing ever makes it to the 2nd floor.
That said, the game was too easy. Snoozefest. I could have spent my time masturbating or buying badly needed presents... but it did use my time up. So okay.
But seriously, those green blobs with their poison effects are just OP. Once they become available, spamming them is a good way of winning most stages.