I love new concepts based on old games. Although I believe this one ought to be called "Earth Defenders" to properly counterpart Space Invaders.
The game is not too hard. Rockets are the main problem, because they home in the little guys, forcing movement into areas filled with pellets, but there is a catch: Their speed increase along their distance from the target. This means that wandering near towers/rocket bases is actually SAFER than keeping a distance.
Rockets can be easily outmaneuvered this way.
The other catch is they always take ONLY ONE target. This meams a tower can be bombarded while some aliens take the rockets. On later stages, there are so many of them, it hardly make a difference. Since rocket bases launch many of them, though, they must be priority target, and when shielded by a tower, that tower is priority.
Other trick: Losing side aliens considerably increases DPS because their fire speed goes up as their allies die. This makes later levels much easier than (I believe) intended by the producer.
Anyway, it's a nice game, had fun. Was made in 2 days, which is also great.