Heh, yeah, I'm a little surprised by how many new subscribers that video has gotten me... And a little overwhelmed. I'm now having to moderate comments, report people making sexual posts at me because I'm a girl, decide whether to correct the people who assume I'm a little boy (who seem potentially the type of people who would give me trouble if they realized I'm female), ignore dozens of sudden friend requests on Steam, and endure idiots posting insults about my review... This was very unexpected.
Congrats for starting your own channel! Please link here when it's ready so we can check it out.
You get press copies of games by asking. I'm afraid I have an unfair advantage, though, because I'm actually a journalist. I am a writer and editor at an educational magazine in this country, for students learning English. It has over 175,000 subscribers, so I can use that when I write to companies asking for press copies. I wrote asking for a copy to review for my magazine and also which I would review on my YouTube channel, and they said no problem, here's a beta key, just please don't publish anything until the game is launched.
However, I've heard it's really not that hard to get press copies even for smaller channels (though how small, I honestly don't know). It probably helps to have a channel with quality content which you can show them, even if you don't have that many subscribers. Maybe do some reviews of games you've already bought, for example, to show your ability to review well. Then just write them (there's usually a "press" or "business" contact email somewhere, or if it's a tiny indie dev, just find their email address) and say look, I have this silly little YouTube channel where I review games and I'd like to review yours. I don't have too many viewers yet, but my content is quality and my viewer base is loyal and growing. Is it possible that I might get a press copy of the game to review? You might be surprised how often they say yes. If you help their game get exposure, it's worth it to give you a free copy. And if they say no, you just keep trying with different games until someone says yes.
And yeah, it's very luck-based, truly. I've been making what I consider to be high quality content for years now, with only the tiniest trickle of new subscribers. I celebrate when that number goes up by one. I did a whole music video to celebrate 100 subs. Then, thanks to my day job, I lucked into an advance copy of this game which was getting a lot of attention. I had time to play it, analyze it, and put together a thoughtful review before release, then as soon as the game was launched, I published my video and a review on Steam with a link to the video. It was the first review on Steam, the first thing people saw, and I instantly got loads of attention. Obviously it wouldn't have worked if the video wasn't any good, though. So... I guess no matter how lucky you are, you can't do well if your quality isn't good, but even if your quality is good, your chances of success are largely down to luck. Unfortunately.