I liked this comic well enough. It wasn't great, but it's much better than most nowadays.
Carl's problem with it is that it's creepy. There's nothing wrong with a creepy comic.* Creepiness isn't exactly new to xkcd. There have been plenty of creepy, funny comics in the past. This comic had math and a dirty joke, what more do you need? Oh, more funny? Well screw you, they can't all be this funny. Again, I think Carl is just trying to find things to hate.
Not that I think we should be giving Randall a break, he's still pretty awful.
*Granted, this is one of my favorite comics, so maybe take that with a grain of salt.