Currently I only watch gaming videos mainly because I don't really know what else to look for that would interest me haha.
I only watch those who are honest to themselves and be themselves in the video, so long as they speak clearly and dont sound half asleep.
I also watch them for the comedy, people with different sense of humours and making fun of themselves or the game when they die or make a mistake, glitches etc.
Anything scripted tends to be a turn off for me and people who "try" to be funny as apposed to just being funny. Theres an honesty or truth about their videos which makes the comedy real and not pre-planned or just too kooky and over the top.
I love to see people make spoofs with the games sprites and characters, and create comedy skits out of them. Something I am planning to do when I have the time. With gaming skits I don't mind if they are scripted or improvised, it's more normal lets plays that I dislike being scripted.
I have no interest in reviews as it often tends to be the commentator rambling about something when all I want to watch is the game and see what it looks like.
I was born with the zx spectrum and master system so I do love retro games as much as new games. But it all comes down to YOU as a commentator and player, that makes me decide if I want to keep watching or not.
branching out I always think is fine. You can appeal to a broader audience. There will be peeps that prefer one over the other but also others that will watch one vid on a given topic and then realise you have videos on other topics of interest also causing them to watch more than just that original video.