The cheesiness of the first one ruined any horror value for me. The second one's gritty psychological tone was much more interesting in both concept and execution, and there were actually parts where I averted my eyes.
Pretty immature concepts though, I mean, there's not much to it after you get over the fact that, yeah, poop is gross.
I am curious to see the third installment, because the director keeps saying things like "the next one will make the last one look like Sesame Street" or something to that effect. The amount that he stepped it up for Human Centipede 2's got me really curious if he can push it any further without going into a different kind of territory. (That is, the extreme sort of genre that incorporates s**t like graphic forced violent incest murder rape into its bodily horror nightmares, which is usually done for "art-envelope-pushing" moreso than grossout entertainment.)