Let me start by saying that I have several Osprey packs, and have never had a problem with quality, ever!
Unlike Petwitzky, I am a huge, HUGE, fan of the Atmos Series of packs. They hold exactly what they are intended to, take you on ultra lite hikes or summer forays. Anything over 50 lbs in the Atmos 50 and the waist starts to dig. So if you want to carry more weight buy a larger volume pack.
Now, as for the Argon, I agree totally, an exceptional pack. I am a professional guide and have tried several large volume packs, from various companies, Gregory (don't ever buy from them), LoweAlpine, The North Face...etc, and I have yet to find a pack that will hold large amounts, and small amounts, for when you are through with all your food, so well. The pack is a bit on the heavy side, but loaded it shines. On several occasions I have taken my Argon and switched it with a clients pack who was having problems. Given them mine and taken theirs. My pack is usually about 15-20lbs heavier, and let me tell you, comfort is not an issue, I would carry an overweight Osprey vs a moderately packed bag from other companies.
The only drawback I can see from the Argon is unlike the Atmos series it has no pockets on the hipbelt.