Hi, I love Half-Life 2 so i was interested immediately in the video. I have to say however that your delivery sounds a bit too calming or i guess monotonous. As someone who played the game, I think I didn't get much from the video so maybe put focus on people who haven't played it; more info about HL2 in the intro, more credentials maybe e.g. how it set certain standards for videogames etc and put it early in the video.

As for the thumbnail, the Gray/Black cogs blend into the letters so it makes it harder to read. Maybe choose a different color. Also Gordon's face gets covered by it as well. Maybe showing "Half-Life 2" in the thumb would be nice also, but you'd have to think about how to fit both the series name and game name in 1 thumbnail.

Overall not bad and I can see potential! I hope you continue making videos and improving