I bought this for my shorter trips.  I can get quite a bit in there.  I'm 6'7" so my clothes are a little larger than the average Joe, but I can get 2 nights worth in easily.  (Plus size 15 tennis shoes).  I like the middle compartment unzips and becomes a one compartment suitcase.  This gives it a lot of room and the straps can help pull it tighter.
However, you have to be careful.  If your airline measures bags, you may not be able to carry on.  I fly SWA and have no problems getting in the overhead bins.