I strongly disagree with charrrlie's comment.
There are so many flash games already where players are able to make progress purely by buying upgrades. I like that there's pure skill involved in at least a couple of them.
Thank you for this Soulgame, it's one of the few games that didn't bore me after 10 minutes.
Although I'd have to say I agree that you should be able to skip the first three levels after you've reached a certain point.
Right-click and select AZERTY keyboard.