That isn't a pre-built computer. That is just a combo special. Basically, you save money on the parts because of the combo deal but you still have to build it yourself.
Anyways, I would always go with just selecting your own parts because those combo deals typically have some parts out of place. As chrisso has stated, the psu isn't that great. However, I would disagree on the gpu. MSI gpus are great. Anyways, the motherboard is also out of place. It uses a more expensive Z77 chipset motherboard which is used for overclocking, but it has a locked processor so you can't overclock anyways.
If this is a gaming build, you can do better than what you have in your parts list. At this budget, you're better off grabbing an AMD processor.