Firstly, if you're from the UK or Europe, you will need a DVD player that can play region 1 DVD's.
The four-episode story arc in the previous series of Moonlighting paved the way for things to come. Series (or season) 4 starts with one of the worst-ever episodes of Moonlighting. A Trip To The Moon indeed! This episode is painful. The script is terrible, and you can sense that the writers had no idea what to do with the characters now they had finally "done it".
A major problem was Cybill Shepherd's real-life pregnancy (later written into the story). Her character had to be written out, which had Maddie de-camp to her parents' house in Chicago. The reason? Because she couldn't deal with her relationship with David Addison. What was her problem? It is David that gets all the viewer sympathy as he is left to mope in LA with Maddie's detective agency to run. Maddie does appear in most episodes, but as her scenes were filmed early on (prior to Cybill Shepherd's maternity leave) there is little interaction with David.
The rather annoying character of Herbert Viola takes over Maddie's role in solving cases with David, though some episodes have no cases to solve as the show becomes more and more like a soap opera. Moonlighting could rarely be described in this series as a romantic comedy/ spoof detective show. Not much detecting, no comedy and little romance.
David again finds himself wrongly put in prison, something that had previously happened in the third season. Yawn!
When Maddie does eventually return to LA towards the end of the series, she has done something so out of character that the credibility of the series starts to come into question.
Bruce Willis is faultless throughout and really carries this series, even though he had his heart set on a career in movies by this point (the first Die Hard film was released in the same year). Cybill Shepherd is also brilliant in the scenes she appears in, but the show appeared to be badly in need of some new writers. A real-life pregnancy to deal with was not an adequate excuse.
For fans only, if you have the first three series/seasons, this is worth getting. However, if you are only going to get one series/season, it certainly shouldn't be this one.