Slate's Sam Adams still has my favourite recent take on crit: "Criticism is the crafting of an argument, not the having of an opinion."
I can only speak for me, but for me, _that_ you dis/liked something is inherently less interesting that _why_ you did. You're selling them on a reading unique to you.
Everyone has opinions, but a great critic contextualizes that within themselves and the greater culture, thus crafting a position on it. A lot of critics forget that.