Your game is really good but does have a few issues, but I can understand since the game is only 25.6KB.
First off, the walls are nice, but seem to be too weak for their price, or for the number of enemies per landing ship.
Second, the warriors are incredibly too powerful, compared to everything else at least. They definitely help, seeing as how the canon is terrible, but they just walk into a row of enemies and the whole row is gone? 15v1? Just doesn't seem like it is possible.
Third, the swamps have no use in the game. They slow down enemies, yes, but they are just too expensive for that, or maybe you should give them a slight damage infliction to all who cross them, that would be a help.
Fourth, the canons. They are way too expensive for being a retarded shooter, and they go after ships before they go after infantry on the land. Also, they have no lead when shooting at distance, so they never hit a ship that isn't coming strait at them. A nice addiction to the game would be the option of controlling the canons and setting a priority target for the warriors/canons(if they opt not to control) so they will target that specific ship/unit first then onto others.
Another thing was the currency, I said everything was to expensive, but you could offset this by giving more cash for each unit killed or like mentioned above, making everything else less expensive. Another thing would to make the canons smart when shooting, or have the ability to buy a more expensive one that actually does work. Oh and one last thing, be able to repair damaged walls, warriors, or canons that are, well, damaged.
The game is good and I enjoyed it, I hope you enjoy the constructive criticism.
9/10, 4/5, 47/50, 93/100.