There are a few creators who have done youtube formats for reviewing comics (more for recommended choices, versus actual critiques), and I think those can be fairly successful if you put the effort into make them fun and entertaining.
Personally, I do a blog format. I like to include example images to break up walls of text and to provide more visual references for those of us that learn better that way.
Whatever the format, it's important to break up your review into categories (ex. intro, art, writing, story, etc). This simplifies the reading experience and can make it easier for you to create a steady pace throughout the review.
The final thing to note is that a critique does not have to be negative. You can teach someone about areas of improvement without putting them down. Critics are important, and we want to be seen in a positive light, not a negative one. Create a reinforcing atmosphere by pointing out the strengths that the creator has, as well as the areas that could become strong with practice and guidance. Do your best to encourage growth, rather than snuff out the flame.
There are many different ways you could create reviews, and I think you need to look for a format that best suits you and your personality. If you enjoy animating, filming, voice-acting, etc. then I would suggest YouTube based videos. If you enjoy talking, but not so much the other aspects, then maybe try your hand at a podcast format. Or, if you are like myself and prefer writing, then perhaps a blog style review is more your cup of tea.
It took me a while to figure out my layout for reviews, and I'm at a fairly comfortable structure currently, although I feel like it can still be improved (and probably will change as I continue to grow as a critic). Don't be afraid to experiment! Try something new and ask others for feedback.
If you ever need help with anything, please don't hesitate to ask! I'd love to help get a fellow critic up on their feet 
Cheers,
WintreKitty
