Ah, zombies. We're all sick of them in games, aren't we?
Nation Red is a game with a simple premise. You're one of four classes each with their own perks and you have to fight off the zombie horde! That's basically what this game boils down to, it's almost exclusively a horde mode. Even the "Mission" mode is just fighting off a series of hordes except the match changes after you hit a certain amount of kills.
What makes Nation Red unique and rather fun is that it's very comparable to twin stick shooters/shmups. The zombies keep coming at you and your goal is to stay alive. Like most shmups, as you kill zombies there are weapon drops, perk drops, and you successively upgrade your character to help you defeat the horde of zombies. There are a couple of maps and modes and the game is excellent fun solo, but when you have four people on your fireteam, that's where the game shines.
This game is excellent for killing some time and the style (twin stick shooter) is a style I particularly enjoy. If you enjoy shmups, if you enjoy zombies, and if you enjoy testing yourself to reach a high score, Nation Red is an interesting twist on tried and true gameplay experiences. It's fast paced and has a couple of modes and maps to make you want to come back.
As a caveat, I cannot really suggest it at its full $9.99 pricepoint, but if it hits a sale/bundle and the style of game is up your alley, you may find Nation Red is just your ticket. I'd also suggest playing with a controller, because, well, its a twin stick shooter and you're far more lethal with a controller in this kind of game than you are with a mouse and keyboard.