Quite some interesting picks. I do have a bit of experience with most of them on some degree, or at least have a basic knowledge what they are about.
Probably one of the favorite games of my best friend. He's been playing for years, and wanted to introduce me into the series as well. I have not personally played the game yet, but I am familiar with the SFM community on YouTube. Right now, as I am writing this, I was thinking about Ceno0 and the Pootis Engage (both part 1 and part 2) series, just for the sake of fun. As for mods, I did hear about the fan-made cross-over with Touhou. Besides, MTB also did a parody of "Meet the Team" videos, but in MMD and with 2hus.
I accidentally got into this series on the 21st of August 2020, after watching Rhythm Heaven Reanimated. At the time, I loved this thing so much, and started looking up online for videos of the gameplay. After almost 2 months, I discovered Nico Nico Douga Ryuuseigun. Here, without expecting, I got my first taste of a little game series turned into memes by the fandom called Touhou Project. Yes, this is what triggered my path towards getting into Touhou, and it all came together just a few days later. That is when I tripped and fell down the hole.
Another game series on the list of my best friend. Even if I never got to play them (still wanna play Half-Life 1&2), I got hooked by the lore, especially about the setting in which HL1 is placed. There's just something very fascinating about the road towards the Black Mesa incident, the fight for survival through the falling research facility (I've heard people saying Half-Life 1 is actually a better horror game then many titles released nowadays, even if the game itself looks dated - unless you play the Black Mesa fan remake), and then everything that lead to the Combine conquering Earth in the 7 Hours War.
Again, another game series I never got to play, but about which I had some slight knowledge. I have seen on of the games live at Asprey (his first livestream I got to see), and I really liked what I saw. The series looks extremely fun, and the story is engaging too.
In shot, there's quite a cool stuff.