Well the first thing you have to know is that you are free to upload any gameplay as long as it has a commentary over it, and not just music to keep you 100% safe. However this is different for Microsoft games, like Halo 4 is the biggest one. You can not upload Halo 4 campaign, and you can only upload multiplayer content without adds unless you are partnered with Machinima, MLG, or IGN (I think Curse and GameFaqs have the license too but im unsure)
Now lets a dress a few things so hopefully no questions have to be asked.
1. Please understand that you are only allowed to upload game content WITHOUT ads under the fair use law. As long as you dont put advertisements on it, you can pretty much upload whatever you want as long as it follows these rules.
1A. Make sure you commentate over the entire video, and stay away from cutscenes
1B. Stay away from music that you are unsure is royalty free or free use (machinimasound.com is a great place for free music)
1C. This is just a tip, stay away from Microsoft games, especially Halo 4, they are issuing out strikes left and right.
2. The main thing you should focus on has a gaming channel is to focus on partnership. Yes the banners are cool but thats not why you NEED a partnership.
A partnership from a large network (IGN, Machinima, MLG, Curse, TGN, Yeousch) will give you copyright protection. These networks have the money and have bought the license and permission to upload game content and put adds over it. So as long as you follow the basic copyright rules as in, music and graphics, its almost impossible to get a strike under these networks.
2A. Be careful about smaller networks. These networks are partnering people left and right and only giving low ads, banners, and zero protection. So dont just go for any partnership, be smart about what you are choosing.
3. You see people all the time uploading their Call of Duty gameplay with monetization and nothing happens. That is because the big developers do not have the time or money to pay a person to sit and flag all the millions of videos that are posted daily. Thats why around 98% of the YouTube gaming population gets away with this, but I tell you its not worth the trouble. YouTube is starting to crack down on the laws so the 98% is getting smaller and smaller.
Like I said earlier, under fair use you can use copyrighted material for non-profit reasons or reviews. There is nothing wrong with that.
So to answer your question you are free to upload just about any type of game content you want (except for halo 4, its iffy with all Microsoft games so just stay away from them) as long as you have commentary over them, royalty free music (you still need a commentary even if you have music) and stay away from cutscenes.
Understand that once your channel gets ONE copyright strike, you will be unable to get that channel partnered or make money off your channel.
I hope this helps and good luck uploading.
*NOTE: I think you can upload BETA multiplayer gameplay 1 day after release. I know that ALPHAS are not allowed to be uploaded, those are often considered leaks and can get you in alot of trouble.
