We stopped by at the end of our trip. For me, it might have been a good stop at the beginning. It does give you a nice layout of the city for future excursions. It runs pretty well and the lines aren't too long. It is $20 to look out windows, but that seems to be the going rate for this kind of thing in other major cities.
Take my advice on one thing, don't do "The Edge". Its a little glass room that puts you out over the edge of the building. Except for the glass floor, the view is no different than from the observation deck and they charge an additional $12. You stand in a bit of a line for your 30 seconds of time and you can't take any pictures because, you guessed it, they take a picture of you for you to buy.More