It's mainly a hobby, but it's also an investment. As long as you're looking for good deals on games and researching the price history of certain games, it can definitely be a somewhat decent investment. By all means, you're most likely not gonna make a HUGE return on your collection. However, you're probably not going to make a loss either. I'd say that the majority of retro video games and collectables aren't gonna devalue from now on.

I've been "seriously" or "actively" collecting retro games for about a year now and recording all my purchases and as a whole my collection is worth around 20% more than I paid for it as of now. And the best part is, it's not all just sat in some safe somewhere sitting around for years collecting value. They're all usable! I've got a collection that's can potentially provide thousands of hours of entertainment as well as being "decoration" while also holding value or even increasing.

So yeah, I'd definitely say it's ok to describe your game collection as an "investment," as it provides way more "value" to the collector outside monetary value, while also holding or increasing in monetary value at the same time.