The gameplay of the original remains intact, but there are various quality-of-life improvements, such as auto-saving, revamped controls, improved UI, and many other details. The game is now also fully voiced for improved immersion.
Edit: It will have a physical release in November Source
Edit edit: releases on Sept 19th. Confirmed using RE Engine
On the Alan Wake FAQ page - https://www.alanwake.com/story/alan-wake-2-faq/ - there’s the following text:
What can you tell us about The Lake House expansion?
Not much! For starters, it’s coming in October.