I agree with you , in part. I feel Team Bondi developed it as a pseudo-open world romp to add to the immersion of a 1940's Los Angeles. As an LA denizen myself, I can't tell you how awesome it is to drive by streets that I recognize (they got all of them down perfectly) and say "Hey ! That's the street where I work! Hey , those are the streets where we got drunk that one time !"
Wouldn't really say I'm disappointed as I didn't really have high hopes for this particular E3. We all knew what to expect already - Uncharted 3, Modern Warfare 3, Halo 4000 by Xbox. I was mostly looking forward to further footage from Nintendo in regards to Skyward Sword