Although living in Melbourne this has been something we never got around to doing until we were gifted a voucher for the early sitting dinner. We chose a Sunday evening starting at 5:30. Typical Melbourne weather meant teaming rain whilst waiting in the shelter for the tram to arrive with a surpising number of people (turned out some were just sheltering from the rain). In the end there were actually 5 trams leaving at the same time which is OK as you are allocated your tram and table number.
Decore is great, cosy of course but comfortable.
The tram ride was quite smooth and took us around South Melbourne, St Kilda etc so lots to look at through the tinted windows.
The food was good and they even catered well for my wife's allegies. Wine, beer and spirits were adequately laid on.
Quality was good but not first class, I do not think anybody could expect that from a mobile tram. Wine was the same OK but not great.
The early sitting (cheaper) is about 30 mins too short and therefore a little rushed. Waiting staff were very good, friendly and even encouraging a bit of a singalong at the end but it felt like the party was just starting when we got to the terminus.
All in all, this is to be recommended but personally I will not do it again except as a treat for visitors which I would be happy to do.
Obviously this is becoming a part of the Melbourne tourist attractions.