It's a one-shot that shows us how the story began... except that it doesn't. It's actually set during the second issue of Marvel Zombies vs. The Army of Darkness, so it starts with Spider-Man and the Avengers already infected. If you want to see how they got that way, read that other series (which is written by John Layman, not Kirkman).
To my surprise, it has Magneto blaming himself for unleashing this plague. If he's right, no punishment could suffice.
Again, this is another Marvel Zombies series with heroic protagonists, so it's horror, not comedy. Nick Fury is the greatest. There aren't many people who'd make his decisions. (Also, since he has no superpowers, presumably he'll just become dead when the zombies catch him, not undead.)
Reed Richards, on the other hand, will make your skin crawl off your body.
This one-shot is short and... well, definitely not "sweet". It's superhero horror. Those two words don't normally go together, but here they do. We know how it ends. The heroes live up to their billing and are genuinely heroic (with one "get the hell away from me" exception), but we know they're all one bite away from joining the horde. If the other Marvel Zombies books hadn't existed, this would have been just another Elseworlds. Memorable, but still just another "what if?" As it is, though, this book's consequences will include the deaths of pretty much every living thing in the universe. Yow.