I think I got this game from a bundle (it might even be that Groupees bundle that sold the keys without legal consent of the developers), and I've been feeling bad about not buying this back in that daily deal in 2012 December. It just wasn't available anymore for purchase...
The memory still haunts me, because this is one of the most enjoyable games I've ever played!

You're essentially twin-stick-shooting and dodging stuff while you're setting up combos in the "DNA chain". It's intense!

PROS:
+ Great soundtrack
+ Great gameplay
+ Enough story to make you want to go on
+ Upgrade system
+ Setting up combos
+ Awesome and versatile boss fights

CONS:
- I don't remember anything negative.

I played 6-8 hours which was the complete game depending on how much I sucked, but this is not my first time playing it.

Definitely worth it. In fact, to make up for having this game via Topware's illegally sold key, I'll just have to buy it again for a friend!