This album sealed the fate for what had once been an inspired classic rock band. At some point after 1978 (the year "Pieces of Eight" was released), aliens kidnapped Dennis DeYoung and returned him to earth with a transplanted brain that could only churn out the most Velveeta syrupy ballads and God awful cheap "jazzy" sounding songs with lots of horn-accompaniment. (See "High Time" on this album for one example). Gone was the Dennis of "Come Sail Away", "Lorelei", "Suite Madame Blue" and the cool rocker "Queen of Spades". We were now stuck with the Dennis DeYoung of "Babe", "First Time", "The Best of Times", "Mr. Roboto", and all sorts of crap in between.
"Kilroy Was Here" is the result of giving Dennis full control of the band's sound in his post-alien-transplant mode. Even a classic album like "Paradise Theater" suffered from some of the worst filler songs ever written (see "Nothing Ever Goes As Planned", and "Lonely People").
Dennis was kicked out in 1980, caused Tommy to leave in 1984, and was kicked out again in 2002. "Kilroy Was Here" is all the explanation you need for that.