What in your opinion, are some of the most/least impressive movie monsters?

In terms of special effects & make up I mean. Both of these crafts have seen dramatic improvements over the years, but some fine early examples include….the original, & best King Kong & Frankenstein’s monster…..as portrayed by Boris Karloff. Advances in technology have afforded the moviegoer a more elaborate, diverse & sophisticated “monster” experience. From Alien to Predator & a host of countless beasts from the horror genre. So, which do you consider worthy of praise? What looked frightening? What….well lets just say lacked a little quality?