Twin Ruin's two core features are the dual color mechanic and rather substantial challenge. Fairly straightforward in mechanics and enemies, but it will keep you busy with what you can do, especially with the color system: you barely hurt things that match your color but their shots can't hurt you at all; however, any enemy touching you does damage regardless of color, so you must switch color aggressively to clear enemies before they get to you, and defensively to absorb bullets.
In the adventure mode (originally, the whole game), you have a small map to search for upgrades as a wall of death presses you to the center, where you'll have the boss fight once the level's wave assault runs its course. The survival mode (a later addition) has you running a fixed arena and spawn list for a simple three minute score challenge, which will really teach you just how [i]long[/i] three minutes can feel.
The core mechanics feel really well tuned and nicely engaging. You aren't slow but you move a little faster when not shooting, so you can run and reposition. You have a secondary heavy weapon that fires from a limited stock, and you charge it by absorbing bullets, turning simple defense into rich aggression. Killed enemies drop pickups that add to score and weapon power, but you have to grab them before they disappear, and nothing waits around for you. You'll get more pickups if you keep your combo bar full, which expects you to avoid getting hit and keep attacking and absorbing bullets. The game signals the colors and locations of enemies before spawning them, so that helps you stay ahead of the moment as waves drop.
You have three characters to pick from (one focus firing, one with a small spread, and one with drones that follow and fire parallel to your direction) and four zones to start from (a few different large enemies and pickups available, with "later" areas harder and a little more complicated). These are unlocked simply by playing and picking up score/power drops, and time required to unlock them all is quite low. No other unlocks or any kind of power metaprogression, so this one plays it fairly arcade straight, which I consider a positive, especially since the game seems tightly focused on quick-burst action rather than long-haul exploration.
Unfortunately, the dev did some restructuring to make the game easier after it was released for a while, and did not keep the original version available. The easier game is still good, but doesn't quite shine as bright as the original, even if it's quite true the original game was crazy hard. I never begrudge players being allowed a more do-able difficulty, but I really wish we had both versions to play.
There are also some minor side tasks the game sets on you each wave (a "wave" here is a whole timed sequence of spawns dropped near you) for a fairly small reward, but the tasks just don't work and are both extremely random whether they are plausible or even possible, and practically require you to ignore everything and play the game wrong to have any chance of getting one before the wave ends. You only get a single task picked for each wave, and every one of the tasks--in both of its color variations--has an achievement attached to it. Those are purely annoying achievements to complete, since you have to get the task you need for a wave, and sabotage yourself trying to clear it before the wave runs out, which may not even be possible. You basically just do timewasting achievement runs hoping you might eventually check another box, which just is not remotely under your control.
The game offers two difficulty levels (easy is indeed very friendly, as you don't need opposite polarity to damage enemies, so polarity only matters for bullet color), and fairly rudimentary options (but you can at least remap buttons), but the price is unduly low and the play feels good and fun, so this seems like a great arcade-style pickup. Plus, we have so few shmups doing color switching to pick from--always good to see that done well.
