It's ambitious to do a day trip to Yosemite, and it's such a beautiful place that you would absolutely want to spend as much time there as you can if you have it. If you have only one day for it though, this tour is a great way to at least see the park.
Booking the tour was pretty painless, and plenty of information was provided to make sure we were picked up at the right time in the right place.
Our tour guide, Dustin, provided a great mix of information, music and humour throughout and balanced it well with time to nap and just take in the scenery. It made the journey seem much shorter than it was! He was also great at keeping everything running on time so we got as much time as possible in the places it mattered. Can't really ask for a better tour guide!
2 hours in the valley itself is really not that long, but the bus stops at a supermarket on the way out so you can pick up lunch and not have to worry about queueing for that in the park itself. Water was also massively in demand - Dustin provided plenty of it, but it's probably smart to bring lots of your own so you don't have to waste time finding it in the valley.
In the valley there's just about time to pop to lower Yosemite falls, enjoy lunch with a spectacular backdrop and do a short loop over the bridges and along the river. It's enough to just take in the spectacle, and combined with stops at Tunnel View and El Capitan you've probably seen most of the big sights. If you're a hiker though you'll be crying that you can't go off on one of the many trails and really indulge in all that Yosemite has to offer.
If I had one niggle about the tour it would be that the 1.5 hour stop at the giant sequoias was a bit of a letdown - it's a long time out of the day and you don't really get to see much given the time it takes to walk down the hill to the grove and back up (if you're quite fit there's a bit of trail to go around at the bottom, but not a huge amount) - and it's time that would probably be better spent in the valley. That said, it's understandable that the tour would want to keep the stops a bit shorter to keep tabs on people and not let them get too far away from the bus and it was still a nice stop! Grateful that it was on the way in rather than the way out though, as that would have been anticlimactic.
Overall, a really great experience and not too ridiculous a thing to do in one day if that's all you have.