One of the finer 2D puzzle-platforming games out there. You have to solve the chambers while avoiding and using the elements of the security system at the same time. The game consists of "worlds", each of which introduces a new element. The cherry on top of the cake is getting S rank in each level. You have to master not just the individual puzzles, but the movement as well, because the time constraint is strict sometimes. The real challenge arrives with the DLC that includes levels an order of magnitude harder than the ones in tha base game. I also found the OST so captivating that I purchased it as well. Unfortunately the servers are down and the community content cannot be played anymore.