I just finished The Walking Dead: 400 Days. Here's my opinion about it:
Nice piece of content, even if way too short. I would have liked each mini chapter to be a little longer, since it's hard to become attached to the characters due to their brief nature. With a little more background on each one and time to get used to them, it would have been much more effective at provoking the emotions it set out to.
I really enjoyed it, but it felt like an appetizer before the main course. Which it actually is. Don't know what else I could say without spoiling anything, so I'll finish with this: if you liked the first season, you can't go wrong with this one. If you didn't, this won't make you change your mind. It may only last about an hour, but it's a good hour.
I agree with you RionaaM. I felt that these 5 short stories made it hard to empathize with the characters and when the time came to take a decisions it didn't have the weight (or the illusion of it) they did on the main story as you don't get the repercusion of your decisions. But obviously the DLC is just a taste of what's to come.