I own two of these Mongo bags (one "regular" and the other a left-hand "S-Type") in addition to also owning a smaller Jumbo Versipack.  I won't get into the details of what makes this a great "man-purse" go bag (many reviewers here have already covered that aspect) but I wanted to point out the following for those interested in buying this product:

WHAT ARE YOU USING IT FOR?
  If you're wanting to pack about as much stuff (especially volume-wise) as a standard college backpack, this is probably NOT the bag for you for two primary reasons: 1) It can't hold a bunch of stuff volume-wise compared to a normal backpack and 2) Even if you are carrying low-volume but heavy items, you will dislike carrying that much weight imbalanced on one side of your body.  For these two reasons, you might want to stick with a backpack (which carries more volume and handles weight much better than any Maxpedition Versipack-series bag such as the Mongo).

  What this bag excels at is a short-haul, low-to-mid volume, low-to-mid weight scenario.  For example, it makes an outstanding 1-2 person range bag (for handguns).  It can easily pack (8) 50-round 9mm/.40 S&W ammo containers and two pairs of hearing protection muffs in the main compartment as well as side and external pockets for additional items (such as: earplugs, iPod Shuffle MP3 player, (2) 16.9 oz regular water bottles, multi-tool, handgun toolkit, lighter, various sized-sticker targets, Uplula magazine loader, etc.).  It can also hold up to (4) Maxpedition dual-magazine holders for a total of (8) spare double-stack magazines using the given hook-and-loop padding in two of the many pockets (both accessible upon releasing the main buckle strap).  Furthermore, the CCW compartment (located in the rear of the bag, closest to your hip) can accommodate a full-size pistol (particularly useful with the Maxpedition CCW universal holster, sold separately) and yet another Maxpedition dual-mag holder (5th one).  In fact, you could probably place two full-size pistols in the CCW compartment (if you forego taking any spare mags in the CCW compartment).  Obviously, this would be very heavy but I've done this on several occasions and prefer this bag than either a conventional, boxy range bag (very unwieldy in comparison) or a backpack (very impractical to access ammo, spare mags, etc. in comparison).  I consider the Maxpedition Mongo the ultimate 1-2 person handgun range bag and because it's built like a tank, I'm fairly sure it'll last quite a long, long time.

  What this bag also excels at is a quick-go bag when I'm carrying low-volume, low-to-mid weight items (like a 15" laptop, iPad, single textbook or a couple of notebooks---not all at once, just to be clear) on short-haul trips (e.g. to a friend's house or running errands in my car).  Anything more and I'd much rather carry a backpack.  Also, it really sucks as a gym bag because while it's much larger than either a Fatboy or Jumbo, it still isn't large enough to easily pack away a full set of spare clothes (shorts, belt, T-shirt, underwear, socks and a HAND towel---not a BODY towel...no way would that fit in this bag with anything else).  It CAN carry all of that but you are literally cramming everything inside very tightly to the point that the main buckle will barely close.  And if you expect to fish around for those items in a specific order (e.g. looking for your underwear first), forget about it.  You'll have to pretty much dump everything out first.  Again, a backpack is still superior for use as a gym bag than the Mongo.

  Also, under no circumstances is this a hiking or backpacking bag.  Unless you're strictly carrying pillows (or anything else super-light), the Mongo serves this purpose very poorly (mainly because it's weight is all on one side of your hips).  I've seen some Youtube videos of guys carrying this in the wilderness and it's laughable at best.

ROOM FOR IMPROVEMENT
  Let's be honest.  This bag is expensive.  Some would say it's very expensive for its limited capabilities.  I have to agree BUT I have some simple suggestions that Maxpedition could incorporate into the existing design of this bag that would improve its limitations:

  1) Maxpedition put ten-kabillion pockets on this thing but forgot to allow the main buckle strap to increase its length (technically, it does lengthen a couple inches but that's all...virtually worthless, IMO).  If they did this, it would allow us to carry more volume and fill out more of those internal pockets.  The main buckle strap, by far, is the biggest reason why this bag cannot pack more volume (and if it was lengthened like it should be, the rest of the bag would definitely be able to carry much more volume-wise).  An alternative improvement would be to get rid of some of those extra compartments to increase room in the main compartment, too (though I'd much rather that Maxpedition just lengthen the main buckle strap because having those extra pockets is very nice).  Either "fix" would be better than the current build.  Lose 1 star.

  2) The Fatboy and the Jumbo (both older and smaller versions of the Mongo) have carry straps but...no carry strap on the Mongo?!?  What a MASSIVE FAIL here.  Maxpedition should have included a reinforced carry handle/strap to make slinging this bag on/off easier as well as moving it around (e.g. from the backseat of the car to the trunk) without the need to lift it over your head.  There is absolutely no reason why this was omitted and Maxpedition should modify the existing design ASAP in this regard.  You may not notice the carry handle until you try one out (on a Fatboy or Jumbo)---and then you'll definitely miss having one on the Mongo.  Lose a 2nd star.

RECAP
  This can be a great bag or a horrible bag depending entirely on what you use it for.  Make sure you consider this aspect before purchasing.