Only one major problem
The gems at either side, which are the hardest ones to get to, don't appear on the screen until they're already halfway past you. That means you don't have enough time to react, and can lose your streak through no fault of your own. I'd recommend widening the screen so that you can't be surprised by a gem that happens to be out of your reach and you'll never get to it because you don't have time.
Aside from that, it's a great little minigame with simple controls, and I like it. But in my opinion you seriously need to do something about those surprise gems at the edges.