The meridian is the perfect bag. In urban areas you just wheel the bag whereas in places where there are no streets you convert the bag to a comfortable back bag. I was carrying the bag for quite a while and there are no disadvantages compared to a "real" backpack.
The attached daypack has a very good shape and you can organize your stuff well because of the intelligent compartments.

I bought this in the ruby color for a very reduced price, but ended up returning it. First, the color is pretty, but much brighter than it looks online. The bag is huge. I bought it because I do a lot of backpack travelling internationally, and thought this would be a good compromise between wheeled luggage and a backpack. I know, I know, the size is right in the desciption, but somehow even though I have a internal frame pack that is very close to the same size (in cubic inches) this bag somehow seems much bigger. With the current airline charges for checked luggage, this would easily hold over 40 or 50 pounds, incurring additional fees. Also the zip-off daypack is not very comfortable. It may get better with use, but it is very stiff, and the top of it rested against the back of my neck in a very uncomfortable way. Probably a small complaint if you like everything else about it.

Got this pack at a deep discount, but in retrospect, I probably would have paid full price for it. The front removable backpack leaves a little to be desired. It is a good size and shape, relatively comfortable, but as stated in other posts, it can be a pain to get into due to the zipper location. However, I understand the logic behind it, so I can deal with it. The size is perfect for a week long trip. The wheels are amazing. One thing I find absurdly helpful is that even when this pack is fully loaded down with my junk, it won't fall over. The balance is great.
Additionally, the airport gate-nazis will let this pack (minus the front backpack) pass as a carry-on.

One disadvantage I've found is that there are a lot of pockets. Personally, I'd rather have one large storage space, but this pack has several (somewhat hidden) pockets that I tend to lose my stuff in. But some people like all the pockets for organizational purposes. To each his own, I suppose.

In response to the above comment, the weird zipper on the detachable pack is designed to deter would-be thieves from accessing your stuff. I like the feature and love the day pack on it's own, both in urban travel environments and on day hikes and bike rides (has a bladder compartment).

I bought this pack used at a STEEP discount I could not pass up, but for me the disadvantage is that I never use the backpack straps and the straps take up volume I could be using for my stuff... oh well.

So far the durability has been excellent and Osprey has very good customer support.

It looks great. Rolls great. It's a nightmare to pack. You have to take the backpack off to pack it. If the zipper ever breaks, you'll be up a very deep creek. To get into the backpack, you have to zip the entire back off. They could have just put a normal opening on the outside and it would have made the bag much better.