I bought one of these a year ago and it is by far the best machine I have ever used. I don't play games on it but according to PCPitstop, who I have just visited (in the interests of the fiorum hive mind), it rocks big time, including games use. It is not the quietest but not the loudest. 512mb is fine for most apps and another 512 stick runs out at £50 ish.
The case is somewhat cramped but with patience and you can muck abbout inside it. At the time I could not have built it for anywhere near the £699 that I paid for it and yours has a slightly better spec.