You know, I have issues with his scores (I have picked on them, ones like Apollo 13 and Titanic particularly, for being eight bars of melody repeated and varied on ad nauseam) and they were not my FAVORITES musically, but I never found any impossible to listen to. I have some scores where if I'm watching the movie, great, but if I listen to them out of context I can't make it five minutes. Horner belongs with Williams, Goldsmith, Zimmer on the list of brilliant CINEMATIC composers. He knew how to write a movie score and wasn't afraid to be musically assertive and thank God he seems to have worked with directors who didn't mind. Listen to the Launch Sequence on the Apollo 13 soundtrack, you KNOW what's going on. And "The Wrath of Kahn" is one of the best Trek film scores (in my head, third behind Goldsmith's TMP and its new Trek theme and Giacchino's reboot, which actually made me all right with new Trek music.) With him and Goldsmith gone I now want 24/7 bodyguards on Williams and Zimmer (thought Williams is 82...dear God let him live long enough to finish the new Star Wars trilogy.)
....Who will ever stand up to James Cameron now? Horner fought for "My Heart Will Go On" (including by cramming the melody line everywhere in the movie and hassling Cameron, scariest director out there, until he gave in.) Not a lot of people in the business fight Cameron on any point and get away with it.