Reading through previous peoples' comments, I'd have to agree.
Brilliant game and yes, I nostalged a wee bit, too. I think it is its simplicity that makes this game so addictive.
As afore mentioned, power-ups, high scores and bonuses would be great. Tweaking the difficulty of each level by increasing difficulty, adding more challenging obstacles and reducing time limits without making a game too difficult too early or too easy can be extremely challenging. That elusive golden ratio, lol.
All-in-all, though, a very cool game, I liked it. 4.5/5, allowing for the areas of improvement which I hope to see in GemHunter II.
Great Job!