Islands of Empire takes the tower defense concept and turns it upside down. The player controls the creep (the fleet of ships) and a Hero unit the player must keep alive during each stage.
The ships persist from round to round, so damage accumulated in one level will be there for the next. A ship lost in one round is gone forever, if the player chooses not to replay the level.
By defeating enemy ships and forts the player accumulates gold which can be spent between levels to repair the Hero unit and any ships in the player's fleet.
Each of the 12 levels (except the first, tutorial level) is procedurally generated. Although if a player chooses to replay a level they will play the same one and not get a new map.
The game gets progressively harder as you get closer to the last level, but the rewards are much greater.