What's $5 worth to you? Is that enough for an hour's worth of The Walking Dead? If so, you should download 400 Days. Don't expect anything more than a momentary diversion, though.
400 Days is composed of five short stories, each from the perspective of a different survivor of the zombie apocalypse. This means that each story is only about 10 minutes long. There's not as much time for puzzles as there was in Season One so most of your actions are dialogue choices. You're introduced to your character and a few others, and then have to make one or more tough moral decisions.
Like Season One, 400 Days isn't much of a game. It's more of an interactive story. The player exists to push the scene along. It's not a test of your skill, then, so much as it's a test of the writers' talent. It's up to the writers to tell a gripping story that distracts you from the fact that you're playing elaborate cutscenes.
Telltale, thankfully, has some strong scribes. In our brief time with each character, Telltale manages to give them distinct and interesting personalities. I'm looking forward to seeing some of these faces turn up again in Season Two. Each story has a sense of urgency and danger. You're being chased, a zombie is eating your friend, and so on. Those tough moral decisions I mentioned are made in the heat of the moment; there are a couple I regretted. I'd do them differently if had more time to think it over, I think.
Are there some false choices in 400 Days? Of course. I'm sure that if I played it through a second time, I'd notice how a few decisions funnel into the same result. However, at the very least, the big choice presented at the end of each story has an effect. Each call you made affects the epilogue that ties the five stories together. Telltale says that these choices will also carry into Season Two as well.
Will my actions in 400 Days have a big impact on Season Two? Probably not. Right now they feel like they did, though. In that hour, I was put into the shoes of people living day-to-day in a bleak world. I was asked the same question five times: "What would I do to survive?" The choices might not affect the next installment of a video game, but they still felt important. That's a credit to Telltale's story-telling ability. They make you care.
400 Days won't give you much closure on Season One. It may not give you much insight into the plot of Season Two, either. However, it's five well-told stories for $5. Even if you look at 400 Days as being completely separate from both seasons of the game, it's still enticing.