Where Simonson really impressed me was his re-imagining of Manhunter with Archie Goodwin, and his one-issue DOCTOR FATE story that really set the Nabu/Kent Nelson difference off, with I believe Marty Pasko's strip. Both had huge influences on how those characters were portrayed from then on, and Manhunter had influence on action-themed superheroics for years afterward.
One of our best artists, and the one who often took the most original takes on established characters. (His Orion comes to mind.)