If you're thinking of starting a replay of the Arkham series in honor of Kevin Conroy, or just to fill the Batman-shaped gap left by Gotham Knights, there are a couple of things you'll want to download in advance. First you should grab Asylum Reborn (opens in new tab), an HD texture pack for Arkham Asylum created by GPUnity and Neato in 2017, and now you can follow it with Arkham City Redux (opens in new tab), a brand new texture pack and advanced launcher for its sequel Arkham City, made by the same dynamic duo and available now.
In addition to updating over 1,000 textures with a combination of AI-upscaled and hand-drawn replacements, Arkham City Redux adds FOV sliders, improves the tessellation quality and distance, and improves the shadow quality. That jagged shadow along on Bruce's neck? It's been smoothed out at last.
Arkham City Redux is available in a couple of different versions. For a lesser impact on performance there's the lite version, which gives you the updated textures for characters and UI elements, but drops most of the environmental textures. It's a mere 1.9GB download. If you want to go in the other direction, the full HD version can be expanded with an alternate textures pack that lets you tweak Batman's outfit, swapping the blue elements of his outfit for black and choosing between threaded, studded, and velvet versions of his cape. The complete version with everything comes in at a hefty 5.1GB.
It's compatible with the Steam, GOG, and Epic Store versions of Arkham City, and there's a Steam guide to installation (opens in new tab) that also explains how the advanced launcher works. Options it adds include adjustable color settings, a toggle to skip the startup movies, and a separate keybind for Catwoman's quickfire disarm. Previously, if you played Arkham City with mouse and keyboard, as soon you unlocked Catwoman's caltrops their quickfire control would replace your quickfire disarm. It also fixes a lighting bug (opens in new tab) in the DirectX11 version.
You may recognize GPUnity as the HD wizard behind Alien Isolation's Improved Graphics (opens in new tab), Arkham Knight's Advanced Colour Correction (opens in new tab), and a Nier Automata texture overhaul that took four years to make. Those four years spent replacing over 300 of Nier Automata's textures must seem like a blink of an eye compared to the six years Arkham City Redux has taken, and perhaps contributed to GPUnity's decision to retire from making HD textures. If you were hoping for an Arkham Origins pack to follow, I'm afraid you're out of luck. As GPUnity explains in the installation guide's FAQ, "I'm done with texture packs, Arkham City Redux is the end for me. I don't have any plans for other Arkham games either. I hope everyone is happy with this mod."