Intrusion 2 [official site] is an exercise in escalation. You begin as a soldier with a laser pistol fighting other men with laser pistols. Then there are multi-pronged snake beasts whose arms pluck you out of the air. Then there are men with laser machineguns. Then the men are riding wolves. Then you can ride the wolves. Then you are fighting mechs with swords. Then you can pilot the mechs with swords. Then there's a helicopter with arms. Then you're sliding down a mountain using the helicopter's cockpit as a snowboard while fighting robot snakes that are busting out of the ground from underneath the snow.
This is, like, the game's first hour.
Brilliantly, every part of every part of the above is powered not by frame-by-frame animation but through a physics system that makes everything reactive to you and the world around it. Once you've destroyed its rotors, that helicopter will pull itself along the ground towards you. Enemy soldiers will take up positions in towers, the struts beneath which can be sliced to make the structure buckle and fall.
The tech and the ambition combine such that everything in the game is simultaneously absurdly overblown and cutely detailed in small, humanising ways. Or put another way, the desperate, clumsy movement will make you feel sympathy for the snake robots.
It's $10/£7 and there's a demo. Heck, you can play that demo in your browser right now.