You need .NET 2.0 to run the game, if you don't have it already.
This is a remake of the "Tower Defence" game, the objective of the game is to defend your civilians for as long as possible.
Enemy tanks will arrive at some time interval, and each level they will get a little bit stronger and a little bit faster. You must defend your castle by placing various kinds of towers at strategic places and making sure they are up to the challenge for the enemy.
Every 10 levels, a "boss" will arrive which requires a certain amount of "preparedness" to meet, but will also give you considerably more money if defeated.
Pressing space bar will skip the time to next level (except for the first half of level 0 before any attacks) and keys 1-4 on the keyboard are shortcuts for the construction buttons on the left side.
Some towers can be upgraded more than some other types, and at each upgrade all the stats will increase by some pre-defined amount, plus some extra upgrade that depends on the kind of tower and the selected upgrade.
Every 100 levels, you advance to the next stage with a new map, and 1 new tower available. So far the game is 3 stages.