Red is a very simple-seeming shooter, but there's enough interesting features about it to make it an entertaining game. Red is designed by Ivory, who also brought you 5 Differences and 6 Differences, and this shows in the aesthetic of the game -- while the design is very simple, it's also very pretty.
In any case, the basic gameplay is familiar to anyone who's played Missile Command or any similar game: you command a turret (located on Mars, hence the name of the game) as asteroids fall. You have to shoot the asteroids before they collide with your turret; if you get hit, it's game over. Your ammunition replenishes over time, so you can't fire continuously, but generally it's enough as long as you're reasonably careful. Of course, it has a tendency to run out just as you're in the thickest of things and need it most. (You can also fire more powerful shots, which naturally chew up a larger amount of ammo.)
The most interesting feature of Red is that shooting an asteroid doesn't destroy it; rather, it merely deflects it. So shooting is not just a matter of pointing your turret and blowing things up; you have to decide where it's best to hit the asteroid to push it out of your way with minimal effort. It rapidly becomes clear that gently deflecting the asteroids to one side is a much better approach than trying to completely push them back up off the top of the screen. Your bullets keep going after deflecting off an asteroid, too; you can set up some very satisfying sequences where, for instance, two asteroids are descending on you side by side, and by shooting between the two, your bullets can bounce back and forth and push them both apart so that they'll miss you.
There are a few powerups which drift by from time to time: shields, which protect your turret from one hit, although you can only have one at a time; a powerup which makes your shots much more powerful for a limited amount of time; and a powerup which adds additional turrets on the ground. These additional turrets fire randomly, and they tend to get destroyed pretty easily, so they're not really that useful (also, they have an irritating tendency to get created right in the path of an asteroid, so they often only last for a couple of seconds). Every so often, there's also a "boss" in the form of a very large asteroid which fills a large portion of the screen.
To add to the difficulty a bit, there's also wind which can (and will) blow your shots astray. The wind starts out light but can eventually pick up to the point where it can blow your shots all the way across the screen, so shooting at asteroids at one side of the screen may be difficult or impossible (however, one thing you quickly learn is that asteroids far away from the center of the screen should generally be ignored, as they don't pose a direct threat to you). Although you don't really notice the difficulty getting harder, when I was trying to get the badge (which requires surviving for 600 seconds) I always seemed to die somewhere in the 500-600 second range, so clearly the game does get more difficult as you go on.
As mentioned before, the graphic design is extremely simple but still pretty, and the background music is a nice song which adds an ethereal feeling to the proceedings. (It also -- and I can't stress the importance of this enough! -- is long enough that it doesn't repeat until after a while, which means you don't get immediately bored and/or irritated by it. Hooray!) That said, the 10 minutes that you have to survive for to get the badge will feel like a rather long time, especially given that not much changes while you're playing the game.
This brings me to my final point, which is only a minor irritation in Red, but will be a major issue in some of the upcoming games in the queue: the timer length is heavily dependent on the speed of your computer. For whatever reason, Red is apparently pretty resource-intensive, so if you're playing on a relatively weak computer, even if ten minutes have elapsed on your wall clock, the game may only think that you've been playing for six minutes (since the length of time in the game is presumably determined by the number of frames), so beware! If you're trying to get the badge on a slower computer, you'll have to survive for longer than you thought. This problem is amplified by the fact that the timer isn't displayed until the end of the game, so I strongly advise against dying just because you think you've reached your destination time. (The game will kill you soon enough anyway; no need to rush.) Anyway, this is kind of annoying, especially since it doesn't seem like Red should be that dependent on your computer speed.
Anyway, overall Red is a pretty game and you'll enjoy playing it for a while, but the fact that the game doesn't change all that much as you play means that its long-term value is pretty limited. Still, it's a fun badge to get.