This is a great pack for the average hiker. If you hike a lot and need room to carry your lunch (and maybe someone else’s) then this is an ideal hydration backpack for that situation.
I already own the Lobo CamelBak. I found that as I carried it both my wife and son drank from it more than I did. It also did not have enough space for more that one lunch. So I needed to buy another one with a little more room for lunches and snacks, and let my wife use the Lobo. I felt this was the ideal pack for my needs.
CamelBak defines the Blowfish as a hiking pack. They defined the Lobo as a bike pack. I personally do not find the labels to be that useful but from what I can tell their hiking packs generally have larger pouches.

How it works.
You have a bladder in the back pouch that is filled with water. You also have a hose connected to the bladder that follows one of the two shoulder straps. This means you have easy access to your water source. To drink you just need to bite down on the bite valve and suck. Since gravity is working for you it does not require much sucking to acquire the water. There is also an on/off valve that needs to be turned on so the water can flow.
In addition this pack has several pouches for extra stuff.

Why should you get one?
Every time I see someone carrying a canteen I cringe. They are not balanced like this pack is. If they are too heavy or the belt is not well made then it can cause a bruise or be hard on your back. And the most important reason is it keeps you hydrated because you have convenient access to water. When you have a canteen you tell yourself to wait until the next time you stop. Well with this system you do not need to stop. You stay hydrated all the time.

How the harness system works.
It is a simple backpack design. You have two shoulder straps. On the shoulder strap you have a clip belt that secures the two should straps together.
In addition you do have a hip belt of sorts. For me this belt rides about 3 inches above my hips. The only reason you will use it is if you run or bike. This way the pack will not bounce around. I only hike with mine so I removed the belt from both hydration backpacks.

Are the shoulder straps universal or gender specific.
Most packs are universal or designed for men. Both the Blowfish and the Lobo fit that category. If you are the better looking of the two sexes then I recommend you buy the CamelBak that is specifically designed for women. There are a couple of CamelBak out there designed for the feminine gender.

How to fill it.
The bladder fits snugly in the back pouch of the backpack. You unzip the back pouch to gain access. You simply unscrew the top of the bladder, hold the backpack/bladder underneath the water source, fill it up, and screw the cap back on the cap. The cap is almost 4 inches in diameter so it is easy to fill..
Unlike my Lobo, you do not have the easy fill feature. Here you have to unzip the bladder compartment and partially remove the bladder so it can be filled. I like the easy fill feature because it make filling a bit easier.

Extra pockets and straps
In this version there is plenty of storage space when comparing it to the average Camelbak.
Starting from the back and moving forward.
The first pouch holds the bladder. It does not have the plastic cap on the zipper like the other pouches do. The plastic caps make using the zippers a lot easier.
Next is the main pouch. It is quite large and can easily hold several medium sized books, camera and several lenses (or 1 huge telephoto), or lunch for 4. It did not fit my 1-inch folder so it isn’t very wide. But it is 18 inches from top to bottom.
The nice feature about the main compartment is it can expand like a blowfish (hence the name.) There is a zipper in the middle of the pack (between the main pouch and the hydration pouch) and once you unzip it then the main pouch expands to about twice its capacity. A very nice feature to fit your needs. Also inside the main pouch is a small mesh pouch. This would be big enough to hold a small paperback book.
The second pouch is big enough to hold 2.5 small paperback books. There is also a mesh zippered pocket inside this pouch as well as a hook to latch your car keys to.
The third pocket is a small external pocket. It is large enough to hold two wallets or a medium sized GPS unit. It is not very big and I doubt I will get much use out of it.
The zippers appear to be durable and they are also capped with a plastic cap that makes it easier to use the zippers.

My opinion on the bite valve.
When comparing the bite valves I prefer the MSR bite valve over this one. I think the bite valve is comparable to my Platypus valve. Ultimately I do not have a problem with it, I just wish the flow rate was higher.

Does the on/off valve work?
It does. At first I thought it was just a gimmick. But this last trip I had a stack of papers I was reading that found their way underneath my Camelbak’s. I did not lock the bite valve unit and the weight of the back on the bit valve caused it to open up. All of my papers were ruined. So I highly recommend you use the on/off valve when you are transporting.

Does the antibacterial bladder material really work?
I deliberately left water in both of my CamelBak’s for several weeks. My Lobo without the antibacterial bladder had an off taste to it. This would be a bacteria or fungus growth. This pack did not have that off taste and the water (which is bottled) tasted just like it did when I went hiking several weeks ago. The antibacterial material works. I still recommend that you properly store this without water in it just to be safe.

My opinion on the comfort level
This is not an issue if you chose to keep the pack fairly light. When I hiked Angel’s Landing I did not feel any discomfort. But all I had was a fully loaded bladder and 6 granola style bars. Not much weight. I know that if I filled it to capacity I would be a little uncomfortable because the straps are not very good and there is not hip support.
The back of the pack is mesh and sectioned off into 6 pads. This increases the airflow on your back and your comfort level. I found that the back was comfortable. The only issue I had was my back still sweated too much and more airflow would have been nice. But I have no idea how they could increase the airflow, at least not without increasing the price a lot more. So I would rate the back as slightly above average.
The shoulder straps also have a mesh material on the inside (the side that is against you.) I had no problems with this design (no itching or discomfort) so I guess they did their job.

Which hydration pouch should you get?
If you want a complete system including the backpack then get a CamelBak pack. Depending on the pack, you will be limited to day hikes and minimal snacks/lunches.
If you already have a backpack that you are already in love with, then get the platypus hydration bladder or the new lightweight MSR bladders. These are great systems, you really can’t go wrong with either one. But both CamelBak and MSR sell their bladders individually. So if you love your existing backpack and for some strange reason you dislike platypus, you can still have a hydration system.
Only get the MSR bite valve system if you are in love with your MSR Bladder or you want a higher flow rate. The valve is a little harder to use but has a higher flow rate then either platypus or CamelBak. The downside is the bladder weights more.

And what ever you do get a bladder made with antibacterial material.

Which Camelbak is right for you?
I would recommend you go to http://www.camelbak.com/rec/products.cfm and use their program to select the pack you think you will want. This can help you narrow down your choices to a couple of models. But I still recommend that you go to a store and check it out for yourself.
Also Platypus has started putting out a backpack/bladder combo of their own. I have not taken a close look at these but it does provide you with another option.

Things I like
The antibacterial material.
Easy to use.
Plenty of space (just be mindful of the weight.)
Hydration for people on the go.
Acceptable airflow on your back.

Things I do not like
No hip belt to help support the weight.
Flow rate not as good as my MSR.
Only usable for limited excursions.

Who is this for?
This would be for someone that takes day hikes and likes to bring their lunch with them. There is also plenty of room for a camera or other gear one may need. Just not enough room for an overnight stay or a daylong hike in 100+ degree weather.

Weight and dimensions
Dry weight: 1.76 lbs
Capacity: 482 cu. in. closed, 781 cu. in. open
Bladder capacity: 100 oz.
(info taken from their CamelBak.com)

How to clean it
Since it is made from an antibacterial material so you should not have problems with off tasting water. But if somehow you do get an infection (which is common with older bladders) then one trick is to make a low concentration of water and bleach. About a tablespoon per gallon of water for 15 minutes should do it. Bleach is inexpensive but can damage your bladder if you leave the bleach mixture in the pouch for a prolonged period of time or if the concentration level is too high. And if not properly washed out then you will have a bleach taste in your water.
If you feel uncomfortable using bleach then go to REI and get their special bladder cleaner and follow the directions. It will be more expensive but safer to use. Several manufactures make cleaning agents including CamelBak.

Accessories
Ice Tubes- This is a deep ice cube tray that makes long ice cubes.
CamelBak cleaning tablets- These are tables that will kill the bacteria that try to live on your plastic. If you do not want to use chlorine bleach then these tablets are a good alternative.
CamelBak cleaning kit- Comes with all the equipment you need to clean out your bladder.
CamelBak hanging rack- Helps your bladder dry out.
Clip- used to clip the bit valve to your strap or clothing.
Hose insulator- Keeps the water in the hose from heating up or cooling down. It is actually something I will get.

Additional note about the versions.
Every year they come out with something better. This year’s model has a better mesh design on the back, and less red. This is typical for outdoor products where they upgrade the product but do not change the name.

Summary:
This is another great hydration backpack from CamelBak. It allows you to drink water while you are still walking or biking. The pack is comfortable and well designed. It also has plenty of room for a full day of hiking, unless you like to take your SLR and 20 different lenses. I highly recommend this pack for the typical hiker. If you bike or run professionally then you may want to look at a lighter/smaller model.

Other outdoor products you might be interested in.
CamelBak Lobo
MSR hydration system
MSR dromedary bag
Camelbak Rim Runner 2010 version. Very much improved.

Recommended: Yes