Let me just start off by saying I love Watchmen. I read the graphic novel and thought it was quite brilliant and thought Zack Snyder did an impressive job making a film version that captured as much of the novel's depth and breadth as was possible while understanding that any movie would have to be, by necessity, an adaptation of the material, as its storytelling can't simply be transferred to screen shot by shot.
To that end, I had picked up the DVD with Tales of the Black Freighter and Under the Hood, short films which tell somewhat peripheral parts of the story which complement the main storyline from the graphic novel. While not in the original theatrical release of Watchmen, they were later edited into an Ultimate Edition, I'm told.
Tales of the Black Freighter is an animated telling of a story-within-the-story thread, originally presented in the novel as a young boy reading a comic at a newsstand. It's reminiscent of the old EC Horror comics (you know, the Tales from the Crypt people back in the day). Seeing the whole story in one blow, rather than as a serial spread throughout the twelve issues/chapters of the novel certainly changes its impact, not to mention its ability to comment on the "real world" action of Watchmen, but viewed as a pulp horror comic story, it still works for what it is.
Under the Hood, originally a series of excerpts from Hollis Mason's (Nite Owl's) biography and reframed here as a 1970s interview/news journalism segment, aims to fill in some of the backstory of the Minutemen and the downfall of the costumed hero in the years leading up to the 1985 of Watchmen, it's mainly going to be of interest to fans of the novel. It does an admirable job of replicating the feel of an authentic television broadcast (even with altered versions of real 1970s commercials), and meets its intended purpose reasonably well. Not essential viewing, but a nice little bonus for those interested.
I should watch and/or read Watchmen again. It's been a while.