Boring with no challenge to be found
This game is a good concept, but I fell it falls short of everything it should set out to do.
My two main gripes are that, one, this is WAY too easy, you get an 'A' for completing a stage at 100%, there's no real reason to strive for an A+, aside from a skin. The levels have no imagination to them, it's simply roll the ball one direction, hope for a big chain. Like one reviewer said, all luck, no skill.
Second, the upgrades leave much to be desired. Essentially the only real upgrade is the ball explosion, and that is lackluster at best. Everything else is something that should be part of the goo themselves. Maybe having upgrades that are for the ball (like increased speed, range, self-detonation, and shrapnel or small bombs from detonation) would've been a better idea.
This is something that shoulder have been thought through a lot more before development.
Also, I think this is a bug, but you actually earn money for each goo destroyed when they're destroyed, not at the end of a level, as is usually done. This makes picking upgrades pointless when you can constantly replay the same stage repeatedly to build cash and have all upgrades before level 3