It's strange that the level ends when you killed all enemies, while there are still civilians to be rescued.. I don't know whether the game was designed like that but that's the only negative aspect on the game imho. 4/5
This is one of the most fun games on kong, really liked it. Sometimes a speed button would be useful, but overal the upgrading matches the difficulty. Would be nice to have some kind of stats for the towers so you really know which one is better. Most of the things which need to be changed are already mentioned in the other comments. 4/5