So I actually saw the Stephen Mangan series before I read the books. Then while I was reading the books I couldn't help but to picture the actors from that series in the roles. (Plus Denis Carey as Professor Chronotis)
Oddly the book describes Dirk as an over weight smoker who always wears a hat. Both these Dirks are skinny guys who never wear a hat and don't smoke. So basically neither of them are the same character from the book. However the Barnett version does mention that his real name is Svlad Cjelli while in the Mangan version Dirk Gently is his real name. Even in the book that was an alias not his real name so the Barnett version did get that part right.
The pilot for the Mangan series seems to be an adaption of the first book with some drastic changes. For one thing there's a white board in the pilot with a bunch of nonsense from a previous case written on it. Among that nonsense is a reference to an Electric Monk and a stuck couch. These are references to the first book. The stuck couch in question belonged to Richard MacDuff in the book. However in the series it's not known who the couch belongs to as we never actually see it. We do know it's not Richard though.
The Barnett series also has a reference to a case involving a couch and a thing with Thor referencing both books. Of course Richard MacDuff isn't in this series. Instead a character named Todd Brotzman takes the roll that Richard MacDuff was in the other series.
Susan Way from the book has been changed to Susan Harmison for the series. This is mainly because she was changed from being Gordon Way's sister to his ex-girlfriend... considering I saw the series first I didn't see anything wrong with them dating but after reading the book and watching the series again I now find it creepy that they were turned into a couple. Her last name was changed to show that they're not related in this version but women change their last name when they get married so her maiden name could very well still be Way.
Anyway both series and the book involve time travel. In the book Professor Chronotis has his T.A.R.D.I.S. which is never called that because the B.B.C. owns the Trade Mark on that name. The character was originally written for Shada in Doctor Who. Dirk Gently took the role of the Doctor and Richard MacDuff took the role of Romana.
In the Mangan series it was Gordon Way who invented the Time Machine as a way to correct a mistake that caused Susan to break up with him in college.
In the Barnett series which seems to have some events of the books taking place in his past, he never mentions having traveled in time before but he does it in this series too. This time the time machine was invented by Zackariah Webb who has multiple other aliases because of all the time traveling. He had to pretend to be his own father in order to explain away the apparent lack of aging.
One of the major differences between the two series is that while in the Mangan series each case is solved in a single episode, the Barnett series spends the whole season working on just one case. I actually prefer it the Mangan way because I don't like the suspense waiting another week to find out what the heck is going on. I like to see the story come to a nice conclusion in just one episode. Maybe some times a two part episode is OK but when every single episode in the entire season is made like that it gets kind of annoying.
On the flip side making the plot stretch out over multiple episodes does allow a lot more time to tell a much better story. Having to cram a big complicated plot into a single episode it often can feel rushed and full of plot holes.
However that being said I think the Mangan series did an excellent job in each episode. The Barnett series however despite being given a lot more time to develop just one plot line I'm still confused by what exactly happened.
The time machine is also used to swap souls between bodies. This cult forms around this machine and they mostly use it to swap bodies with celebrities. This a famous singer named Lux Dujour. His soul gets forcefully transferred into a nobody named Gordon Rimmer (not to be confused with Gordon Way.) The thing is... Gordon seems to be Lux even before they switched souls. His attitude, his mannerisms, even the dog he seems to care for all remain consistent for the entire series... and at one point they even time travel back to before the switch was made. Was that suppose to be a flash back and that's why it doesn't seem like he's any different after switching souls? If that scene with Lux and Gordon switching souls was suppose to be a flash back they didn't really do a very good job of indicating that.
I also felt like there was some stuff that actually didn't connect to this case. That shouldn't happen when Dirk's whole thing is that everything is connected. There's a whole bunch of stuff that seems to be going to entirely separate case for a second season which the original series never got. So not only did they make me wait a week between episodes to see the end of this case but there's still more stuff that I have to wait I don't know how long till season 2 starts to find out what the hell is going on.
It's a good idea to keep the audience interested so they'll want to come back to find out what happens next. However it's really not a good idea to leave any loose ends when you have no idea if your series will be renewed for another season or not. They could decide not to ever bring this back and then this loose plot threads will never be resolved.
Also I tried not to give away any major spoilers when writing this. I did mention some things but taken out of context none of it's going to make any sense unless you already know what I'm talking about. So which do you prefer Stephen Mangan or Samuel Barnett? (This is the TV/Movie section so Book Dirk isn't really an option.)
For me it's a pretty close call. They both do things I like and things that kind of bug me but I think I prefer the Stephen Mangan version.
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