The controls are probably the game's best feature; they are super responsive, so both platforming and shooting (after you're able to reach your first weapon) are easy to do. Level design follows the Metroid plan of allowing you to reach certain areas only after you've obtained a certain ability or finished an objective, and it's very well-done. The story is somewhat vague (you play as a robot tasked with saving a "biosphere"), but it's told in a fairly clear and interesting way.
The game is only 99 cents, and the developers have said that future episodes will be released for free to current owners. With that in mind, you're probably getting even more game than you're bargaining for. If you're interested in the action/adventure genre at all, definitely pick it up and give it a play-through. If the rest of the episodes have as much effort put into them as this one, Grokion could turn out to be a real standout series on the iPhone.