I enjoyed this one. It was trickier than Mondays often are, and had some nice stuff like SWAIN (29A: One who goes a-courting) (I wanted "Froggy," but it didn't fit!), and VOLTA, clued much differently from the way it was yesterday, which was kind of cool. Things like ENOL (16A: Carbon compound) still trip me up, but there wasn't too much of that.
The theme was simple and clean, although I kept reading the first Across clue as "... and a homophobic hint..." which threw me off for a bit. I liked the "four Is" theme, and I also liked that none of the theme answers had any other vowels at all. Also, could you think of four more disparate pieces of fill than INHIGHSPIRITS, NIHILISTIC, GINGIVITIS and STRINGBIKINI? I doubt it.