I like him and Kershner because they questioned George like anyone should. It is still Lucas' vision, and he deserves most of the credit, but Kurtz to me seemed to keep that adult nature to Star Wars that it lost when ROTJ & the Ewoks arrived.
In one interview I read from 2002, Kurtz said Lucas changed after Raiders of the Lost Ark. It is a classic action movie, but it is just that, a 2-hour action bonanza, with not the greatest plot to go with. Lucas realized, and he was right, that if you give people a wild-action ride for 2+ hours, people will come. To me after ESB, that is where Star Wars took a left turn, from great films to good ones.
Watching ANH & ESB, you can put them up to classic movies, and have a healthy argument. After ESB, you start saying:
ROTJ: The last 40 minutes are awesome, but those damn ewoks, and that jabba scene goes on way to long! And who is a that singing that awful song in Jabba's palace, was that in the original or special edition?
TPM: Jar Jar? Jar Jar? Jar Jar? It still boggles my mind 6 years later!
AOTC: Great action once the clone wars start, but that love story, argh! And what is up with C-3PO cracking jokes during the clonewars!
ROTS: Definitely got back to the original Star Wars, but Padme dying of a broken heart? Can Anakin's turn be any less convincing? "NOOOOOOOO!" Where is Qui-Gon, can you possibly spend a minute explaining the force ghost trick?
It is interesting to read Kurtz's quotes, and I'm sure there are sour grapes between him & Lucas, but he definitely helped the first two films rather than hurt them.