After scouring the web for Grand Canyon tours, we settled on Viator because of the volume of reviews. Every single one warned of a *long* day. I would second that...but our LONG day was 18 hours from pickup to final drop-off!!!
The pickup bus came right on schedule at 6 a.m. We were all herded into the headquarters and given instructions and a simple breakfast (juice, danish, coffee). Though they were organized, we didn't get rolling until 8 a.m. Our driver was very knowledgeable and gave good information along the way. Our late start was exacerbated by a road delay along the highway for about half an hour. The Hoover Dam was impressive but we were very rushed. There was a quick McDonalds break and finally lunch at the National Geographic Center. The food wasn't bad, but we certainly were rushed to eat and then catch the IMAX movie. There was no time to browse the center before boarding the bus again. We made our stops at Mather Point and Bright Angel Lodge as scheduled, but only getting barely an hour at each stop, rather than the 1.25 hours advertised. This is not enough time to really take in the scenery and compose your photos. The Canyon was gorgeous but you always felt rushed, especially with my wife terrified we'd miss our bus (the driver gave dire warnings of $900 bus rides back if you missed the pickup).
Coming home there was a driver switch. This fellow had a heckuva time remembering all the hotels and forgot to drop us off at our hotel (after several reminders). We finally got off at the nearest stop and was able to walk back, fortunately. By then it was midnight and we were exhausted.