Several friends, when they heard I was visiting Melbourne, urged me to check out the Great Ocean Road. My usual approach is to rent a car and go it alone. Then I noticed on Trip Advisor that there are a number of tour providers. It appealed to me because to really enjoy a coastal road it is helpful if you do not have to keep your eyes on the road.
The awesome part of being a tour group member in a country where they drive on the left: if you grab the shotgun seat you have a beautiful view of the coastline! This road was developed by boosters of tourism after the Great War and employed mainly returning soldiers, fondly called Diggers for their role in digging the trenches. Even today Australian soldiers are sometimes called diggers.
1. I chose Melbourne Coastal Tours. For a reasonable $130 AUS the company picks you up at your hotel and gives you a full day and then delivers you at a location you request in the central business district (most of our group wanted to be dropped at a restaurant not their hotel). Our tour guide Daryl was excellent and I learned a lot more about Australia’s history and geology than I would have on my own. It is also more fun to explore with other people.
2. We made frequent stops throughout the day. The first stop for bathrooms and morning tea at a small town on a protected ocean inlet was about 1.5 hours in. After that we stopped about every 30 minutes until we were on our way back to Melbourne. It allowed us to see wildlife, rainforest, and coastal beauty and enjoy shopping, a delicious lunch at La Bimba and hiking. It was a full day!
3. The breathtaking beauty is worth the investment of time. Although if you have difficulty climbing steps, your access to the beaches and some of the other stops will be limited.
Melbourne Coastal Tours also does penguin viewing tours of Phillip Island.
americanjulie.com 
Glad you enjoyed the GOR. My favorite part is Loch ard Gorge!