You know those things you sometimes buy, and you love them so much you wonder if maybe you should buy another one just in case they stop making it? That's about how I feel about this bag. It's so good.
There are plenty of great camera bags out there, especially a few from Lowe that are nice, but after seeing video with Andy Mann explaining the features of this thing, I was sold.
The two main things that make it such a great bag are:
1) Sling style -- allows you to just slide the bag from your back, under your right arm, and it's right there in front of you, ready to go. The bag is designed so this functions fluidly and in a way that it feels connected to your body.
2) Top opening -- after you've slung it around to your chest, you can just leave it there, open from the top, and grab all your stuff. I frequently change lenses, which, before now, meant trying to find somewhere to set lens or cap down while doing it. With this, you have a few nice little slots in the bag where you can just leave the extras while you change, and it's all safely contained. It's really great, and I never worry about dropping anything.
I keep my body and LARGE wideangle zoom on it (Sigma 18-35 for size reference), and two medium sized lenses in other compartments. I could easily fit 2 more lenses in there if you divided it efficiently.
I also keep a card reader and cable, an extra battery, a few filters, an extra card, tripod quick release mount, and a few other odds and ends in it, with room to spare. The main pocket is well designed and deep, the outside organizer is nice for a phone, a pen, a snack, or smaller camera odds and ends.
I have only two minor quibbles:
1) After a long day, my left shoulder starts feeling a bit sore. Just one of side effects of a sling, nothing too major.
2) There's no place to hold a tripod! I have a travel tripod, which is moderately light, and it throws the balance of the bag off, but still, it would be nice to have the option.