Native. The game will use your desktop resolution upon first run, but you can set it to any res you like in the options.
Vastly Hor+ with slight horizontal squash. The wider the aspect ratio, the more the squash.
(For this DR I assumed 4:3 was the baseline as usual, but the game may have been primarily developed for 16:9 actually. See screenshots on the official sites.)
The first-person view seems strictly Hor+. (It's hard to demonstrate with screen caps as striking any button/key in this part will reposition the camera before the character moves one step forward. Feels definitely more strictly Hor+ to me than the third-person view or cut scenes.)
The slight flaw in the way the game adjusts the FOV to the resolution has no effect on the gameplay in widescreen.
There's no real HUD, except the 'radar icon' (white house drawing on top of the screenshots below) which scales correctly. All texts are animated drawings and seem to align their size on the display's width : the wider the aspect ratio, the bigger the text.
The inventory screen scales correctly.
Real-time rendered cut scenes are Hor+/squashed.
