I don't think they've done anything other than add DLC. Hell, it's been over eight months and things like mirror reflections are still broken.
This is not 100% true : AI has been patched (it's not F.E.A.R. AI level but it's serviceable), frame pacing has been patched, they added races, cars and guns.
It's also a tiny bit less glitchy but I believe the engine is unpatchable lol.