GemCraft Chapter Zero

One of my favourite games from last year was the addictive tower defence game GemCraft Chapter One. This year the makers have created the prequel to it - Chapter Zero. If you're anything like me then you'll have forgotten that the original game was loosely fitted around a storyline - and this game is a continuation of the same storyline backwards. I for one was certainly wondering how all these gems obtained magical powers and this instalment sheds exactly no light on my puzzlement.
Anyway, Chapter Zero is very similar to Chapter One, but with a load of new levels, a load of new enhancements and a load of new bonus towers on each level.