Okay, here's my shot at it.
The film is set in the present day. Since the events in Ghostbusters II the Ghostbusters have never been out of business. They have always regularly received calls however in recent years business has dried up a little. Ghostbusters is not making the money that it used to. The business is hanging by a thread, the taxman is on their case and they are just keeping their heads above water.
Venkman and the others are only a few years away from retirement and are hoping to hold on until then. Venkman is upset and disappointed that he never got what he wanted. “To be rich beyond his wildest dreams”. He has a bitter hatred towards the government, the city of New York, and the countless lawyers which have bled his business dry over the last few years.
But his luck is about to change. A business man from a local cable channel approaches him to talk business. He wants to make a reality television show which follows the Ghostbusters on the job. Venkman is a little reluctant but the man makes him an offer that he can't refuse and he accepts and signs on the dotted line.
The only thing is, Venkman hasn't told Stanz, Spengler and Zeddmore that they are about to become the nations latest reality tv stars. He breaks the news to them but they are strongly opposed to it. Whilst they can understand it from a business point of view they do not want to be on television and they realise that it is far too dangerous to have a television crew standing by.
Due to the fact that Venkman has already given the tv producers his signiture they reluctantly have to take part in promotional adverts and photo shoots. They want to strangle Venkman!
The television crew show up at the firehouse nervously waiting in anticipation for the next call. They have with them hair stylists and makeup artists who attend to Spengler, Stanz and Zeddmore as they seethe with anger. They wait and wait and finally Janine Melnitz receives a call.
The Ghostbusters pile into the Ecto 1 and screech around the corner with the cable satellite van following behind. They get to the address and film the Ghostbusters catch the ghost. Venkman loves the camera but Spengler, Stanz and Zeddmore hate it. The editors spend an eternity beeping out all the swearing!
The show is a huge success! Rated number 1 on cable. Everyone's tuning in but when the ratings start to drop the boss gets involved and starts changing things and things go pear shaped for the Ghostbusters.
The employers of the Ghostbusters begin deciding what they want them to say and even start giving them lines to say in each episode. They tell them were to stand and how to acting. They want the Ghostbusters to do too much and although their show is at the top and the Ghostbusters are making heaps of money from their tv work their ideas for the show are putting everyone in danger.
Venkman and Spengler, Stanz and Zeddmore have a talk and decide that they will give the producers of the show an ultimatum. Either they will do it their way or the show is finished.
The shows producers accept. They then plan on doing a live episode of the show. The cameras follow them out on a bust and broadcast it live. The job is more dangerous than they thought it was going to be and takes the presenter of the show. Venkman saves her but is then killed on live television due to the irresponsible nature of the crew.
Venkman is dead. The show is taken off the air and the Ghostbusters are angry and extremely upset. They attend Venkmans funeral and after a few days they pull themselves together and start working again. After they come back from a job they have their dinner together and are startled by the appearance of Venkman who has found his way back as a ghost.
Venkman looks almost identical to his living persona except he is slightly transparent. He's scared and confused and once he is assured that they won't bust him he asks of their help. He tells them what it is like to die and where he ended up. He explains that he was judged by an otherworldly being who sent him to his deserved place for eternity. He says that Heaven and Hell are just two ends of the spectrum. There are many places in between which you can be sent to depending on how good or how bad you've been in life. Heaven is like a 5 star hotel and 1st class travel where as hell is similar to a concentration camp. Venkman tells them that he somehow escaped and found his way back to the world of the living.
The Ghostbusters want to keep Venkman in the world of the living even though he is a ghost. Venkman just wants to be treated like a normal person again. He wants to be able to go for a walk in the park, to go out to eat and to do his grocery shopping without scaring the life out of other shoppers. Stanz, Spengler and zeddmore want to keep him inside the firehouse because they get calls whenever he walks outside the door! They even rush to a bar at one point only to be confronted by venkman at the bar having a drink. Venkman just wants to be left alone.
Unknown to Venkman the Judge has sent two demons to find him and bring him back. The Ghostbusters find out about this and capture the demons.
Spengler discovers that the capturing of the demons was a very big mistake and that they have now put the world of the living in danger of biblical preportions. Spengler knows that they must let the demons free and that Venkman must go back to deadside. Venkman reluctantly goes. The Ghostbusters say goodbye to him.
Spengler devises a plan. He and Stanz engineer an electronic gateway which allows them to step into an universe. They select the universe they want to step into similar to changing channels on a television. Spengler, Stanz and Zeddmore know that if they manage to bring Venkman out of the special gate which they have created venkman will once again have a living body. They go insearch of Venkman, find him and save him.
At the end Venkman smashes the cameras and of the tv crew and punches the tv boss.
That's just off the top of my head and is all I have for now.