I started playing some Ion Fury.
It’s super fast and normal difficulty’s a fair challenge, at least for me. The game seems like an excellent entry in its genre, and I probably don’t suck at it too much, but I’m mainly there for the levels and looks, not for the shooter mechanics. I somehow remember Duke 3D as being less frantic than Quake 3, but clearly I must remember wrong. Perhaps it’s that Ion Fury isn’t quite playable keyboard only (unless you tried easy mode), while Duke 3D is.
Ion Fury is the TWP of '90s shooters. It plays like how you remember Duke 3D. To put it like TWP did, it was forgotten in a drawer over at 3D Realms back in '97.
You need to find keycards to unlock doors, turn levers, and carefully manage your resources. Actually resource management is getting on my nerves a bit, causing me to do a lot of quicksave/load in case I spend too much health or ammo in an encounter. Very historically accurate, I suppose. 
The weapons seem somewhat pedestrian, even if they are well executed caricatures, at least for the first three (humongous) levels. A revolver, a shotgun, a grenade launcher, an SMG (dual once you find a second), grenades… I understand we won’t be seeing a shrink ray or anything like it even further on.
The seamless way the levels connect into a larger world is nice. I’m actually kind of curious what the true system requirements of this game are; I think I might give it a try on my old 2010 netbook to see how it runs.
Playing it in UHD might have elements of cheating, but given the game’s frantic nature and resource management I don’t mind the occasional minor advantage. In some of the larger open spaces you can clearly see enemies that can’t see you, so you can take them out with your “sniper” revolver. You may not be able to see those faraway enemies in HD, and playing it in the “intended” 640*480 would give you a massive difficulty boost.
It’s also a very clear demonstration of how nonsensical it is to say that a game designed for 640*480 can’t profit from UHD. It’s only up close that textures are pixelated, but you can see so much beautiful detail in the distance.
I encountered only one clipping bug so far, but I wasn’t really looking. I remember encountering them more often in Duke 3D. Luckily it was a rare instance of breakable glass, so I could escape from my prison.
When I quit last night I was stuck trying to find the exit from level 3, or at least (presumably) the last part of it.
I took some fun screenshots using my regular methods, but alas, they turned out white. So I can’t show you floating shell cases. (Floating due to a fan, not due to a bug.)
Oh yeah, and the game’s only 100 MB.
If you have any kind of fond nostalgic memories of Duke 3D, the game is probably worth checking out. But I’d say this game only takes the level design to new heights, not the enemies, weapons or any other part of the gameplay (save for headshots). The enemies are starting to feel a bit repetitive and I’m at most halfway through.