Build your base, defend it against the Titans, explore new stuff in the tech tree and then: do it all over again in the next challenging level of Revenge Of The Titans. It is as simple as that! But it is also very addictive gameplay. By now I have clocked in more than 50 hours ingame, more than I can say of other (more mainstream) titles. The concept of tower defense games may sound simple to you, but make no mistake, the learning curve for this game can be steep sometimes. At least, you can always go back a few levels and experiment with other items in your tech tree and then spend countless hours trying new tactics with different weapons. However, should you be stuck on a particular level, you can always ask around in the steam forums, the developers are very active there and give excellent insight into the game mechanics (e.g. why you should upgrade a turret, how to maximize profits from mining crystals, etc.). To cut a long story short: I love this game!