Baseline (Widescreen) Solution & Issues
The game was Vert- out of the box; patch 1.02 added native Hor+ support. So patch the game to the latest version, then simply select your desired resolution from the Graphics Options menu.
Screen change is Hor+ with Vert- player weapons. The HUD is squished in non-16:9 widescreen ARs.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Compass falls off screen, with flawless widescreen works perfectly again.
Eyefinity / Surround Specific Solution & Issues
Patch the game to the latest version, then simply select your desired resolution from the Graphics Options menu:
-move the resolution slider until you find your desired res amidst all your standard, widescreen and multi-mon res's.
-hit Apply, quit and restart the game.
TH2G DE users: in Win7, I was unable to run the game at 5040 and other custom resolutions, even with DX10 FX turned off. All res's are available to me in XP, though.
Screen change:
Hor+ with a number of flaws...
-player's weapons are Vert- and move to the sides of the display.
-the HUD stretches, the objective pointer arrow is off-screen.
-water drops (when standing under leaky ceilings) are oddly magnified.
4k UHD Specific Solution & Issues