Those are basically glorified likes. A like is also equally evident of an engaged reader.
I guess these at least specify the kind of emotion the comic evoked in you. But now I'm imagining myself commenting these word for word on every comic that makes me feel this way (because there are only so many ways you can write "Broke my heart" in 3 words), and then the authors realise I'm commenting the same things on other comics and feel like I'm being ingenuine. That's admittedly an unlikely scenario though; maybe I just need to be less paranoid :'D