Descent 2. Where to begin. In my humble opinion, it is the greatest shooter of all time. The story is eerie and compelling, the enemies intelligent and cunning, the gameplay thrilling and dynamic. Each world feels totally different than the last, with twisting labyrinths full of enemies, power-ups, hostages, secret passages, complex door/forcefield/wall locking/unlocking systems, incredibly fun boss battles, and the infamous guidebot. With six degrees of freedom, barrel rolls, afterburner, and brakes, the skill cap of Descent 2 is sky-high. There's a certain complexity to movement and dodging that only flight games seem to require.
On top of that, this isn't an open sky game like War Thunder, there's plenty of barriers to hide behind, doors you can ope n/close and traps you can set for enemies to run into. You can trick the enemies into hurting each other, combine different tactics such as activating a forcefield and using it as a barrier with guided missiles, you can even use robots as robo-shields to protect yourself against its comrades' attacks. By having elements of flight combat sims and traditional fast-paced shooters, Descent 2 is one of the most challenging, exciting games out there. The modern competitive scene is extremely skilled and you have to have reflexes as sharp as a fighter pilot to succeed.
The art, animation, and robot design is beautiful and intriguing. The variety of robots you face have a wide plethora of behaviors, acting individually, sometimes as a swarm, and sneaking up on you with near-human level combat comprehension. While this game may be very old, there are plenty of mods available that create taxing high-def textures and very realistic particle animations. Your $1000 graphics card won't be able to keep up when fully modded.
An enormous single player campaign, limitless potential with multiplayer, an active competitive scene, incredibly beautiful mods, and the most innovative FPS gameplay ever, makes Descent 2 a game worth far far more than a traditional $40 or $60. Oh wait, it's only $5? ONLY $5?!? If you don't buy this, you're a complete fool missing out on PC gaming's pinnacle game. 5000/10 is my rating for Descent 2.