There are a lot of DP playthroughs, but the gold standard are the two I am linking below.
First, for comprehensiveness and completeness, nothing beats Supergreatfriend's Let's Play Deadly Premonition, a 47-part playthrough that shows literally everything in the game. Supergreatfriend plays the original version on the XBox 360 and has a very wry delivery that makes watching his playthrough very enjoyable. He's also PG-rated, which is good if you want to watch the playthrough with your kids.
For those of you who want more humor and hijinks (with a lot more salty language), the other amazing series of videos is Two Best Friends Play Deadly Premonition. This 34-part playthrough is full of hilarious moments as the two YouTubers (who are no longer friends, unfortunately) discuss the game and mix in their own personal anecdotes and opinions on all things pop-culture and gaming-related. If you didn't follow their channel you will be lost sometimes, but I quickly got into the groove with these two and enjoyed all 17 hours of their playthrough. Note that these guys play the Director's Cut of DP.
If anyone knows of any other really great playthroughs of the game, let me know.
Also, if there are any amazing playthroughs of the sequel, post those as well.
there doesn't seem to be anything here