This is a good sized bag, with out being huge.  It will hold everything you need for baby with enough space to hold keys, phone, and wallet for mom.  I love the included stroller straps and changing pad.  Enough inside pockets to organize diapers and wipes instead of just throwing everything in there.

It's spacious enough to use for an overnight bag, but compact enough to use every day.  Love this bag.

EDIT: I have been using this bag for well over a year and there has been minimal wear on it.  The lining around the top edge has become a little worn and resulted in small holes, but it doesn't cause a problem for us.  I received this bag along with a Vera Bradley diaper bag and I much prefer this one.  I'm not sure about the other complaints saying it's awful quality, because nothing has gone wrong with this bag.  I've tried out quite a few in the last 5 years and this is my all time favorite.