If Wolfenstein the new order is anything to go by for high resolution gaming, it's the textures and meshes/models are going to be enormous, otherwise it will just look like crap...

Reminds me of looking at the N64 intro for one of the zelda games, in low resolution it looked okay, in higher resolutions on PC through emulation, it looked laughable...

Games that work well with no extra effort needed:

Aliens versus Predator Classic 2000 works well (some text scaling issues - subtitles and objective text).

Assassin's Creed works fine.

Risen works fairly well (some text scaling issues - object and NPC names).

Risen 2 works fairly well (some text scaling issues - object and NPC names).

Rogue Trooper works fine (very minor text scaling issues - location names in cutscenes).

The Witcher works fine (might crash if you have the in-game antialiasing option enabled - force MSAA on it through your graphics drivers instead if you still want it).

The Witcher 2 works fine.

-----
Games that work, but may require some effort:

Slave Zero works fine at 3840x2160, just run the nGlide settings tool / configurator and set the screen resolution to "By desktop" (and set your desktop res to 3840x2160 before running the game). The game doesn't support widescreen FOV (without modifications), so set the aspect ratio for nGlide to 4:3 to avoid stretching (you'll get black bars on the sides).

-----
I tested most of these games using a 3840x2160 custom resolution through Nvidia Control Panel, and some using Nvidia DSR (4.00x factor). Some may work better on a native 3840x2160 display.