uuhhh my post is all messed up...
I can understand why a few of the things about the Brain Bag might be
frustrating. I use(d) the Brain Bag on a regular basis when I was in school and have mostly retired it at this point, however for overnight trips, etc. it makes a great traveling companion.
I shared your initial feelings on the front top pocket, that it should be
larger. However, over time I learned to use that pocket for (what I feel)
it was meant to be used for - a place to throw small items for easy
access. I think it's the ideal pocket for keys, change, chapstick, cell
phone, etc. If it were any deeper you'd lose all of those small precious
things.
As far as organization is concerned, you should check out some of the new
pouches and organizer pockets that are available. Combined with the
Freudian Slip it might solve your problem.
The front pockets are additional organizational space if you are willing
to use them. The Brain Bag doubles well as a carry on bag but it wasn't
designed as a carry on bag. If you are looking for a carry on bag you
should check out the Aeronaut. (I've used it, it's GREAT! =)
Sunga already responded to the umbrella holder (which is great for those of us living in the great wet northwest) though I can completely understand why it would seem a little odd!
The sternum straps. They can be a little annoying. I never used them much, so I don't really feel qualified to comment. I'd imagine they could use to be a bit sturdier, and, like Sunga mentioned, removable!!
I hope this helps a little and I hope you continue to use and love your Brain Bag (mine has sadly been replaced by the Buzz and the ID, but I still use it on occasion.)