To call this game "Tetris on a sphere" would be a bit disingenuous. It's far, far more complicated than that. Tetris merely requires you to place falling pieces such that they create solid, dissolving rows and thus abate, if temporarily, the peril of becoming overwhelmed by the steady stream of burdens in what I can only assume is a clever metaphor for adulthood. Globulous, on the other hand, has a clear goal: clear out layers of the sphere and reach the prize inside. It's the method that gets complex.
The gameplay is a little difficult to grasp at first (as is any puzzle game that operates in 3D), but thankfully there are plenty of tutorials. The basic concept is very similar to Bejeweled in that you have to match multiple, concurrent pieces in order to remove them from the game board. You can shift an active piece towards others like it, so long as they don't intersect with shapes of a different color (except the blank gray squares). Ultimately, you'll burrow throw the layers and reveal the cream-filled center and move on a level. However, much like Mahjong, You'll be dealing with pieces on top of others and have to figure out which ones are and are not playable tiles.
Globulous probably isn't for everyone; if nothing else, most people don't tend to think in three dimensions (how many of you regularly look up without a reason?). However for $0.99, it's a bargain for a simple, light-hearted puzzle game. Also, in an interesting move, the soundtrack to the game is available on Bandcamp here. This is a really clever way to augment revenue that other developers would be wise to follow. I'm looking at you, Santa Rockstar.