Vickicat
I was thinking of doing let's plays but ultimately I decided to do Twitch live streams instead. It has worked out pretty well and I think I've gotten a lot more attention on Twitch than I would have on Youtube. I'm trying to play a variety of different games on there to attract more followers. Also planning on playing some games for comedic value on there (like really bad cheap games I find). Honestly though what I think has drawn a lot of viewers to my channel is that I'm female and play stuff that apparently women don't typically play. One of my viewers pointed this out to me. It's definitely worked in my favor. I guess if I can give any advice I'd say just try to be creative, or do something outside the norm, play a game that might not be expected or just find something you can do that sets you apart from the rest.
This all said and done though, if you do go with the live stream route, you can still do the youtube uploading as well, just seperate your stream into 25-40 minute stretches and call it a day.
You could even use artwork, either via commission or from a fan, as an opening still graphic for the video and continue from there.
Games that are overdone:
7 Days to Die
DayZ
Pokemon (randomizer, nuzlocke, etc)
Minecraft
Call of Duty series
Super Smash
Games that have too much stuff out there already but are also very old by internet standards:
Persona 4 (original, not Golden)
Persona 3 (original, FES, and Portable)
Shin Megami Tensei 1-4...
Pretty much any Atlus game.
Games that have very little but are difficult to cover because of how the game is designed:
Monster Hunter