I'm not a heavily publicized game developer, but as a passionate designer I still think I would have some insights in this area.

Of course I'd ask you to cover the genre and my favorite parts of the game during your review. I would love to have a spotlight on my bullet hell's story/characters (being a passionate storyteller and fantasy enthusiast) and bullets (because of the genre). 

When it comes to the developer's preferences, it's pretty case-by-case. Maybe asking them if there's anything they want you to cover would help beforehand. But when it comes to the genre you can probably make a good guess, as Halkind mentioned earlier. Bullet patterns for bullet hell games, movement for platformers, 360 no-scopes for shooters, you name it.

But beyond that, I'd love to see some of your unique thoughts thrown in. My views about my games are skewed by perfectionism and hours of hard work that gives me a feeling of emotional attachment to often times irrelevant systems. For example, I recently built a dialogue system from scratch that I'm more proud of than my bullet hell system sheerly because of all the hours I spent optimizing it and working out its kinks... and my game's a bullet hell game. Depressing, right? 

We need external viewpoints to keep ourselves in check, so some comments directly from your perspective would be incredible as well. Something honest, even if it means blatant criticism, but also hopeful - suggesting improvements instead of tearing the game/developers down.

See what stands out to you, good or bad (preferably a mix of the two), and share your thoughts. This gives you a chance to develop your own style and give developers feedback they wouldn't normally expect... which is almost always awesome to have.

Hope this helps!

What I expect from a YouTuber who comments on my games is, above all, respect. Respect for my work, time and passion in developing the game. Unfortunately, this is not a given. I've seen YouTubers make fun of my games online without bothering to play them correctly, just for "entertaining" their audience. This is akin to shaming a person in front of an audience when they have no means to defend themselves. I have had better experiences with reviewers. The most important thing for me in my games is the story. I want feedback on it first. Is the story compelling? Are the characters well-written? What about the choices and their consequences? Comments on the technical aspect of the game are, of course, also welcome; I am not a programmer, and I am aware that my games may have technical deficiencies. I'm happy to receive tips and try to improve the game technically within my means. And thank you for asking. I hope you leave a link to your channel; I'm curious about your future video game reviews.

I wouldn't care if a review of my game spoke well or badly of it.

In my opinion, there's no such thing as bad publicity, only poorly managed publicity. A clear example of this is how many games have become famous solely because of scandals.

I suppose how to talk about a video game is instinctive; it's still an intellectual exercise. 

Above all, I think sincerity is to be appreciated: there are content creators who only say what they think people want to hear, what will get them views and positive reviews (YouTube is full of such mediocre channels). And that's why they align themselves with political correctness, so as not to offend people of glass, who are the most irascible and reactionary.

If someone were to review one of my works, what I would appreciate is sincerity. Should my work be mercilessly criticized? So be it. You learn from criticism, or from sincere praise, not from the fear of offending political correctness.

Good reviews need constructive criticism !

If a part of the game as issue, talk about it and explain why it's an issue. If a part is good explain why you like it.

As a game developer, a good review explains what I did good (and why) and what I need to improve (and why).

As a player, a good review explains the good and bad parts of a game (and why; just like the review for developer) and also avoid spoilers.

When I receive written review I copy-past the review in LibreOffice Writer and turn green the section about good parts, red for the bad, orange for the minor inconveniences and blue when the player didn't like my design choices. A video review should give enough details to color code the time stamp in a similar manner.