I read a number of previous reviews here, which steeled my expectations to get my face whacked by branches and to be deafened by nonsensical juvenile recorded guides. I used the NYC pass for travel for 1 day, which essentially gave me time to take the Downtown and Uptown route once. The Downtown route took 90min to 120mins. The Uptown Route took about 90mins. The starting location for the Uptown bus is no longer in front of the Major Deli (as indicated on the site and brochure), but a few streets down as the bus driver will tell you. The buses in front of the Major Deli are now the drop-off point.
There is no live tour guide as others have said. Audio recording is OK and there is plenty of voice acting involved to help spruce up the information, The information is not detailed, but you do get tidbits of interesting points. The downtown route audio seemed to cutoff a few times when heading downtown due to hitting the next point before the audio from the previous point finished. The return route had few stops, but more audio. The uptown route had a lot of audio and none of it got cut off on our ride. No one got hit by any branches on either route, though I could reach out high enough to touch a branch, so maybe the local council has trimmed the trees since.
You can't ride the bus around and around as the bus drivers will tell you to get off. The wait time for the next Uptown bus is 60 minutes, whereas it is shorter for the Downtown buses. I was already used to riding the MTA's subway, so the Big Bus was more of a chance to see NYC in open and on the surface, which it was great for. Some attractions are a bit far or difficult to see (eg Statue of Liberty) and will be dependent on traffic lights and whether the bus stops long enough for you to catch a glimpse (eg Brooklyn bridge), Empire State Building.
For me, this attraction was a great way to get that windswept hair look and to breath some of that NYC fresh air. Others enjoyed it as a way to get a feeling of the city without having to walk or take too many stairs (since riding the subway doesn't let you do that, even if it is mostly cheaper, faster and more convenient).