You know, with the level ending with lava pouring into the flooding waters and turning into obsidian each section, does that mean the world is gone? :P The gameplay had a good balance of difficulty in making you feel the pressure of time, but it never felt like you didn't have enough time to complete the level. I never deleted the pieces as it felt like it took more time to do that than to put down new blocks. The boss mechanic does change up the strategy slightly, but only downside is there's not really anything different between the levels in terms of strategy. Overall, simple and effective design.