Could be better
While the game has that certain retro factor (Loved the intro!), the game itself is kind of a letdown.
First of all, this game is pretty hard. The controls for left and right were pretty straight forward, but having the message about jumping over lava pits *after* hitting a lava pit was kind of cheap. It didn't even occur to me that collecting the gems is the only way to knock the boulder back until I filled the mysterious 'K' bar for the first time.
And this leads to what I felt was the biggest problem: some of the gems are impossible to get. Either they are all the way on one side, so even the roll isn't helping. Also, having the rock already scratching your heels and waiting for a gem only to find that none is to be seen is extremely frustrating. Especially after I found out that the gem can also be behind a rock. The hefty deduction of the knock bar for missing a gem combined with these is a pain.
Graphics on the level are also quite bland after watching them for a couple of minutes. Some added detail would be nice.
Overall, just some tweaking on the mechanics would make this an awesome game.