It should be fine for low-mid tier games. High end games like Metro 2033 or Crysis you'll definitely have to turn a few things down though the 7770 is a pretty good GPU.
.. To be completely honest you did over pay by quite a bit.
I built the same spec PC on newegg to compare, the total was about 580 though the PSU was of course different since you didn't specify exactly which model.
680 with Windows 7.