Bumping this thred from the dead, but still free.
However, trying it out immediately turns to regret by mission 4. Difficulty spikes there, and doesn't let up, and you only have (by that point) two towers. However, this isn't the entirety of it. Oh no.
Tower upgrades are governed by stars, esrned by doing tasks and missions (up to 3, controlled by completing said mission at certain health thresholds), and, of course, microtransactions. However, because the difficulty spikes incredibly and rather early on, this becomes more of a pay to win game almost immediately, and with no remorse. Upgrades also increase in cost, and you will, most likely, not be able to keep enough stars to upgrade ahead enough against the challenge. Repairs also come back (Which is still as dreadful as ever for a TD game), but repairs are also far more frequent, and become an annoying pain in the ass extraordinarily quickly.
Also, the screenshots lie to you. Half of what the game advertises in visuals is false. Hero units don't exist. Upgrades are bland two-trees lines for each tower. Even the second map has been reportedly unplayable as well.
It's good if you don't mind the dreadfully impossible difficulty curve, which is notorious with nearly all of Melesta's games, but if you do mind it, then do yourself a favor and ignore this. It's another unfinished, half-assed product that Melesta rushed to nab sales.