While not bad, this password system not as secure as you think that it might be. It can be hacked given time and resources since a dictionary type attack could be used.
Throw in a few numbers and punctuation if you want a much more secure password.
Well I would have thought a brute force hacking program would take forever to crack a sentence... I will put commas and full stops in next time, I will make a whole paragraph! Nothing will crack that!