Watchmen: the complete motion comic - 7.5/10
I never even knew this existed until recently, but obviously it's good because it follows the Watchmen plot so closely. Some minor things are left out, I kept thinking they left out this line and that line, and even a couple of my favourite lines were absent. It's all right though. The animation wasn't particularly stunning, but it doesn't have to be. The artwork is pretty close to that in the comic (Dave Gibbons was responsible for artwork) so no disappointment there. It's all narrated, by one person in a limited range of voices, but all speech balloons etc. are on the screen so you can just read them. They could have used a different narrator for female voices, but they didn't.
For relative comparison, I would give the comic itself a 10/10. If you don't want to read the comic, I'd say watch the Zack Snyder film instead (me? 8/10), because I expect this would be harder to appreciate if you don't like/haven't read the comic. Do I think this was better than the Zack Snyder film? Yes and no. Much less is left out, and Nite Owl looks like an owl again. That said, it's five hours long(!) (split into 12 chapters, if you wish to watch some and come back later) and doesn't feel the same as reading a book, so I think if you don't already love Watchmen, you're not going to love this. Alan Moore is a fantastic writer but that plays out better on the pages of his books.
I have to say though, I wish I'd seen this earlier. I did a motion comic for my final art college project, and this would have been good for reference.