What's to dislike about Knull? Well, the retconning and overexplaining of the symbiote lore and history was unnecessary and I don't like much of how it has turned out. Also this huge King in Black crossover isn't something I'm interested in. He's a God that is a threat to the whole Marvel universe...? Yeah, no. That's not something I wanted/needed.
I'd have been fine with him popping up as a badguy for Venom to tangle with in the Cates run, and maybe have him be super-powerful and have a history with the symbiote (but not a "everything ever related to the symbiotes comes from me, and oh yeah, I'm also where Gorr got his power too" kind of history). I don't really care about a symbiote god being a company-wide crossover threat though, even though I love the symbiotes and their old lame history.
Oh, and I dislike the overly-toothy elongated mouth that he gets drawn with quite a bit. It doesn't work for me.