I watched your youtube trailer, and one thing I noticed a was how your voice work was very monotone. It's a problem I struggle with myself, it comes off to people as being 'disinterested'. Talking with confidence, and picking up the speed of your read and I think you will start getting more subscribers.
I would say your channel art is very basic. It's a good start, but seeing it's a call of duty page, incorporate something in there that feels call of duty. If there are issues with using artwork from call of duty, you can get around that. Get some stock images of grenades, guns, ammo etc. cut it out, add some life to the page.