Tried to play this on my Mac and nothing got installed. Then I switched to Windows, which at least worked. However, sometimes my clicks didn't register and there's no option to exit the game.
As for the game itself, it's a matter of chosing upgrades and waiting for cooldowns. Since all units share one cooldown and all spells share another, it makes the most sense to maximize upgrades on one unit and one spell. That way, you can spam that unit and spell until the enemy is beaten back.
The AI isn't brilliant. It obviously just has a shorter cooldown and more advanced units. The only real challenge is trying upgrade setups until you find one that works on each level. Otherwise, it's just a matter of clicking buttons the split second the cooldown ends. Bizzarely, the spell and unit cooldown are the same length of time. So I guess there's a small level of strategy deciding which you ought to click first.
Given a glut of free tower defense games with better conceived mechanics, there's no need to give this one a second look.