There's some companies that have said you can commentate their game with no problems (Blizzard)
There's some that will sue you for even something as small as putting their system startup sound in a video (Nintendo)
And most of em are somewhere in the middle.
You're gonna have to be specific about the game you want to upload.
Find the maker, the publisher and then google to see if they've made statements reg this or sued ppl.
You might also want to look up "Fair use policy" and, if you're going to do let's play style videos, the concept of "transformative".