We normally get 30" of rainfall per year ... I think we've had 10" in the last 10 days and we just started our rainy season, so waterproofing is a priority.
By way of review, the bag is plenty big for a 24-72 hour BOB at 25liters. My son has already packed it with sleeping bag, tarp shelter, and all of his bug out gear, to include handguns & ammo.
Pros: easy top loading design. Padded shoulder straps, hip strap, chest strap. Has a tie down area on the outer face, and two smallish mesh pockets on either side for things you don't mind getting wet (holds a stainless steel flask perfectly). It also has an interior zipper pocket that's flat and hangs against the inside back of the main compartment, large enough for passport, wallet, etc.
Cons: no backboard/pad. no hydration sleeve or means to use one without compromising waterproofness. no molle/tie downs to hang additional satchels, etc. Its a little more work than a normal toploader to get at the main compartment.
All that said, it holds alot of stuff, and if you pack smart, you won't get dug in the kidneys. I'm 6'4" tall, 225# and it doesn't feel like a kiddie pack to me - I'd happily use it; my son is 6' 150# and it fits him like it was made for him.
So after my initial infatuation, I've decided to keep my 5.11 Rush 24, but get an OP Stuff Sack for the main compartment, since my current layout uses molle and a hyration bladder. However, if I didn't already have that, I'd have ordered this Overboard Bag and been just as happy.