My first thought was 'oh my god, this is going to be a looong day' but it ended up being the perfect amount of time you need. There is just the right amount of stops, and just enough moments of silence from the guide to get a quick nap in on the bus ride home.
We had a great tour guide who made it more personal by joking about where each of us was from and knowing a little bit about each place we were coming from. The scenery is gorgeous! It is impossible to get a bad picture on this tour.
When we stopped in Loch Ness, unfortunately the boat tour wasn't running but we got a good lunch at Bothy Pub, sorry I think that is what it was called. I would only suggest, use your time wisely at Loch Ness because the time goes very quickly and it is just so great to see.
It is definitely well worth the cost, and you would be crazy not to do it.
The only problem we had was with the people in the office in the morning of the tour. They had put the tour in the wrong name so we had to stay outside to sort it out and by the time it all made sense we were the last ones on the bus and had to sit apart in single seats and they were the seats right between the windows. Once the tour started though, all was good and we had a fantastic time! I highly recommend this tour!