To point out now, I ended up playing the game all the way through, then going back to beat all the special expert levels until I reached 1500 points, the highest possible. I must have played the game for 5 days non stop, but it sure felt good seeing that space shuttle blast off after beating 150 levels of Gubble madness. The graphics in Gubble are simply astonishing, whether you are looking at stills or floating over top of a robot infested board. The interface is simple and consistent throughout, even when you are going between levels. Sometimes they reveal secrets in the level that you normally would not see if you just skipped the animation and started drilling away.
Enemies range from the simplest moving gear, to a Gubble seeking missile launcher armed robot.
The variety of enemies really adds to the fun of the game, since many of them are mixed up in the levels, not all the same in one. Those are only a few of the tools though, there are many more that you will be presented with before the end of the game. Try hiding in corners to avoid enemies. Here's one of the tough special levels. Don't think that when you have beat the last level in the game that you are done.