Tower of Guns is the best FPS / Procedural Death Labyrinth I've played.
There is no hitscan, every weapon requires you to lead your moving targets, and every projectile can be dodged. You are very mobile, and upgrades you find in the tower will allow you to become even faster and stay airborne longer, if you're really lucky you'll be zipping around and rarely touching the ground.
With each new run you'll chose a weapon and perk to start with. Weapon mods found in the tower will allow you to change how your weapon operates, such as giving it a shotgun spread or causing your projectiles to seek or bounce. These, in addition to the reusable items you'll find and various stat increases like health, speed, or jumps, give each run a unique feel, even when you start with the same build. If you're lucky you may even find new, unique weapons in the tower that operate unlike anything else you can start with.
The tower is partly procedurally generated. Each floor you visit has a theme and you'll fight through a random assortment of rooms in that theme before fighting a boss. While the content of each room is random, the rooms themselves are handmade with a better sense of level design than you get with most procedural games, including secret areas and easter eggs.
If you're like me and scour the levels for hidden items, a successful run will take about 35 minutes. You cannot save in the middle of the game so you'll need to finish it in a single run. Thankfully each run is fairly short and can lead to a very addictive one-more-try game session.
Check this game out if you like old-school fast-paced shooters.