Hexothermic isn't a terrible game. In fact, it's not even all that bad. It's just not really worth any sort of monetary transaction when there are Flash games out there that provide the cathartic chain reaction experience for no cost whatsoever. Despite a solid aural presentation, the visuals drag the production value down and the lack of anything truly outstanding means that Hexothermic will be highly unlikely to hold one's interest for more than ten minutes.
By all means, give it a try, since it's worth that much. Whether it's worth more than that, however, is questionable.