He didn't write the Thor script, he was just a consultant. I believe Ashley Edward Miller wrote it.
I love B5 dearly but JMS' runs on Superman and Wonder Woman were godawful. And while I enjoyed his Spidey run (well, the first 2/3 of it) the whole thing was a rehash of B5. Right down to stolen lines of dialogue.
And I thought "Call to Arms" was awesome!!!