West Virginia has also been running this defense for the last few years and they've done quite well with it.
The key to the defense is that it allows the defense to use multiple fronts and alignments which often times disrupts the offensive line blocking schemes. Most teams that play the 3-3-5 don't just sit in the base alignment, they can stem to all sorts of looks like 3-4, Bear, 5-2, 5-3, 4-3, 6-2, 4-4, etc. Some of these EA has added to the game such as the Bear and the 4-4 look.
The key to the defense lies with the two strong safeties. These players are generally aligned near the line of scrimmage against traditional sets with a tight end and two backs. They can easily get into an eight man front to stop the run, drop eight in coverage, and of course use all sorts of combinations of dogs, blitzes, stunts, and coverages.