I think intros aren't very fun to watch, and you should make sure the first few seconds of your gaming video are unique and interesting. But it can help reinforce branding. I think it works better for tutorial videos, which might get a lot of views but less viewer retention/subscriber growth... but for a gameplay commentary channel, I feel like if you do a variety of games, people will keep coming back for the let's player's personality and not a flashy intro graphic and dubstep.