We visited previously around 11 years ago. Although the park has 'downsized' from its former glory there is still so much to see. And now its free entry!
The tramway train ride is worth paying for (diesel engine only - the steam engine is apparently broken). You will get a good view of areas of the park that are otherwise difficult to walk to and may even spot emus chasing the train. You will also see some former attractions now idle and in disrepair eg. the water wheel and sawmill, and get a sense of what this park could be like if restored to its previous state.
Good shoes and all-weather gear are recommended in the cooler months. Lots of walking on hilly terrain and mostly unsealed surfaces (some of us actually prefer this type of walking). Most of the park is not particularly wheelchair or pram-friendly - check their website for details.
Some of the buildings were closed but you can still get a look at the historic displays through the windows.
There is a Tourist Information centre set up in the entry building so you can pick up brochures for other Gippsland and Wilsons Prom area attractions.
The entry building also contains a small shop where you can find diverse items ranging from energy meters and energy-saving power-boards to historic books and local products such as honey, preserves, cordials and wine.
Staff and volunteers are friendly and helpful. They even have a Coal Creek 'credit card' which you can use in place of cash at the little stores in the park (leave your credit card or drivers license as ID). Just pay the total at the entry hall on your way out.
For those arriving by car.. note to driver: Sections of the drive from Melbourne to Coal Creek are East-West aligned and if the weather is sunny then sunrise/sunset driving will be unpleasant due to maximum sun glare. Try to drive outside these times to avoid the problem.
Further note: The roads near Korumburra are a bit pot-holed and uneven, once you leave the major highways.
Yet another note: the signs could be better.. once you enter Korumburra follow the 'i' tourist info signs and they will lead you to the park (or use your GPS/Navigator).
On that topic, check mobile phone coverage on the internet before you start the trip. We found very patchy or no reception in the area. Ironically, there is a sign in the park to call an after-hours number if you get locked-in (eg if you didn't leave by closing time) but there is no public phone if your mobile doesn't work.
In spite of all this it is still worth the drive. Pick a dryish-weather day, pack a lunch, plan a relaxed drive with breaks in the little rural towns en-route, and allow plenty of time to explore the park and enjoy.