In a word, this game is lacklustre.
Although I can't say it's a terrible game, I certainly can't say that this is a good game either. I felt that it was visually overstimulating, with too many flashy graphics making it difficult to see everything that's going on. Basically it's full of substanceless flashy graphics which actually hinder gameplay instead of enhancing it. It's quite a short game and it's by no means a challenge. The few instructions that exist in the game are poorly written (or translated), which says to me that no one really cared too much. I found the lava walls a little questionable when the controls aren't precise enough and a safe distance from them a matter of trial and error every time.
The objective of the game is to capture areas of the game screen. You are safe from most creatures on your baseline (though not all). You dash out and try not to get hit by enemies, and once you capture 75% of the original area, you win the level.
If you're looking for a game of this sort, then I would strongly recommend you consider Fortix2 instead (which also has a section that includes the Fortix original levels in the Fortix2 artwork). The Fortix games are more challenging (if you play on hard), more engaging, have more levels, are better thought out, and last but not least, they're a whole lot more fun than Lightfish. Also, I think that the Fortix games on an easy difficulty setting are easier than this game because the controls and game mechanics are better.
I've enjoyed the game for a few hours, but I'm not sure it was worth it. Depends on what $5 is worth to you, how bored you are, and how much you love this sort of game. It also will not work on my Mac.