This gun rocks. I have owned an F4 illustrator GS for about 6 months now and i have not had a single problem. The Stock barrel is very nice, i can hit a 12 ounce can from 30 yards with about 2 shots, very consistant. The Expansion chamber is great. I have never frozen the gun and during a 6 hour day the fps span has never gone over 15 fps. This gun has won many games with me. This gun competes with even the best of them. I have schooled quite a few autococker, angel, shocker, and other thousand dollar gun owners on frequent occasions with this bad boy. Put it up against any spyder or tippman and it will win every round. I hardly ever have any ball breaks. I can go through an entire day without a single break, many times in a row. If you are looking into getting this gun, look no further.
The gun is somewhat loud. It also has a heavy trigger pull, but what blow back gun doesn't. It is also pretty expensive, but i got mine off ebay new for 180, so if you look around you can probably find it for a lot less than retail price.
This gun has all sorts of goodies and upgrades. I would take this gun over any other blow back gun anyday.