Guy has made 4 movies, only one of which was any good (Guardians 1) — but it wasn't great; just unexpectedly fun. Guardians 2 was a lot weaker — obvious jokes, still no romantic chemistry, lame ending, boring Rocket B-story, etc. Had some fun parts but nothing about it screamed "Guardians 3 must be made by James Gunn because no one else can pull this off."
Slither was a mildly amusing mediocre horror comedy. Never saw Super, but no one seemed to really like it. He also directed part of Movie 43, which is considered to be one of the worst Hollywood movies ever made.