For those looking at the Xbox 360 version for achievements, it will take about 25-30 hours to collect and do everything needed for 1000/1000. Very fun game, so it's not too much of a chore at all (other than being a collect-a-thon). I'd recommend it to anyone wanting a solid single player experience, especially at this price.
From my experience Gamefly ships all games with original cases and manuals too, so that's a definite plus.