Halo 4 does indeed look stunning at times on PC, however, there are still a few issues that need to be sorted out.
1. The lighting on the final cutscene of the mission "Reclaimer" is completely broken and does not accurately reflect how it looked on Xbox 360. This issue was present back when I played through the campaign on the original Xbox One version of the MCC, and I'm sad to see that it has been brought forward to the present.
How it looked on Xbox 360:
How it looks now:
2. The Banshee does not feel good to control with a mouse. If you try aiming straight up or down, you need to repeatedly drag your mouse up or down, or else the Banshee will "straighten" itself out. This makes it very difficult to aim low at enemies below you. Also, you're not able to move your crosshairs during the middle of a Banshee flip, however, once the flip is over the game seems to automatically adjust the Banshee's direction to an input you may have entered in the middle of the flip? It's hard to explain, but it does not feel good. Try flying the Banshee in Halo Reach and doing some flips while trying to adjust your aim mid-flip, it is night and day compared to how it currently is in Halo 4. This seems to be accurate to how the Banshee controls in the original 360 version, but it doesn't translate well to mouse controls.
3. The Scorpion turret controls with a mouse are back to the awful sluggish controls from Halo Reach. Y'all got this right in every other game! Load up any mission with the Scorpion tank in Halo 3 and once again the difference is night and day compared it how it currently is in Halo 4.