It is safe to assume that Gabe Newell is a frequent player of PC games. He almost certainly enjoys exploring new titles, analyzing game mechanics, and staying abreast of the latest trends in the industry.

As a successful technology entrepreneur, it is highly likely that Gabe Newell has a keen interest in technology in general. He may enjoy experimenting with new gadgets, exploring innovative technologies, and following the latest developments in fields like AI, robotics, and virtual reality.

Since establishing residency in New Zealand, Newell has shown appreciation for the country's natural beauty and culture. It's reasonable to infer an interest in outdoor activities and perhaps local arts. Also supporting New Zealand film and technology industries.

Given his background in literature (which fueled Half-Life's narrative), he could be a reader, and even of sci-fi or fantasy.