Pretty good game. Level 28 is awful though because you have planets which are near the same color as the background, although they're not exactly 100% the same. But you basically have camo planets. Got all the way up to there then lost all my lives because of that. You can probably get through if you pick up enough shields or have enough lives.
There was also another level earlier on which was bad because blue planets on a purply-blue background, but not nearly as bad as that Level 28.