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!