The aim of Stack Rocket is to build a rocket tall enough to reach space, one section at a time. Each new part slides left and right above the tower, and you decide when to let it fall. Drop it on center and the rocket stays steady; drop it off to the side and the structure starts losing its balance.
Patience is the main skill. Wait until the sliding part is nearly in the middle before releasing it, even if that means letting it pass once or twice. Only Up Parkour has the same appeal of seeing how high you can get, with climbing instead of stacking.