Baseline (Widescreen) Solution & Issues
Native support for 16:9 and 4:3, but you need to set the aspect ratio from 4:3 to 16:9 in the options to get the proper aspect ratio for widescreen. There's a 20(?)/30fps cap.
The crosshair is squished horizontally.
Attached cheat table is for testing only and is not a fix on it's own.
To remove 20-30 fps cap use patcher from the attachment.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
The game can run in 3440x1440. However, it only lets you choose a 4:3 or 16:9 aspect ratio so it's stretched.
I've attached a cheat table for anyone who wants to try getting other aspect ratios to work properly.
Eyefinity / Surround Specific Solution & Issues
4k UHD Specific Solution & Issues