Here's why:
* Slippery can be negative in some contexts (like a slippery slope), but it can also be neutral (like a slippery surface).
* Slick can be positive (a slick move) or negative (a slick salesman).
* Wet is neutral.
* Slimy almost always has a negative connotation. It suggests something dishonest, untrustworthy, and potentially dangerous.
Let me know if you'd like to explore more words and their connotations!