It's hitting me harder than I'd have expected, I think it's partly due to how much fun his videos always are and how positive he always seems to be. Even going back and rewatching his earlier videos of his cancer updates, he still has me laughing (and now, crying too) at his self-directed morbid jokes. The Great Potato War is on my top ten of all time (if not top five) youtube videos list: he's hilarious, the optimization is insane, it's such a trivial thing it seems it could only be done for the love of the game, and it also reminds me of what it's like when I'm optimizing a piece of code. Just hunting for the smallest advantage in the most obscure places. It's just sad to see someone who's brought so much joy to so many people go through that.
Usual caveat that I don't know him as a person, only what he shows through his videos, but even the fact that he worked to keep his identity unknown draws me in more: he wasn't in it for the money or fame, he was just a guy who loved the game and loved sharing it with others.