It's strange, because I love those sorts of movies, the "so bad it's good," the old B-Monster flicks in particular (like The Stuff).
But Sharknado didn't even achieve that affect for me, I'm just sitting there looking at a badly animated tornado passing over trees that don't even have the decency to blow in even a slight breeze. Among other random nitpicks, particularly the house on a hill that flooded... when there was absolutely no water outside of the house. The second one definitely had me laughing, though.
I guess it's a given with how SyFy is infamous for atrocious CGI and special affects, but I'm thrown off by how much they're trying to push the movie, they've played the damn thing about twenty times by now. Kelly and Michael were the ones I died at though.