Good, but not quite the 100th issue spectacular you might expect-
Issue 100 of Journey Into Mystery finally hit the news stands one crisp morning in January of 1964. It closed out both the plotline concerning Mr. Hyde's sinister plans, as well as Thor's petition to Odin to have Jane Foster granted immortality. While it was a better than average Thor story, from both a writing and art perspective, it failed to address one major point - how was Mr. Hyde able to disguise himself as Thor (last issue) and rob a bank?
The backup stories - 'Tricky Travel' and 'The Unreal!' are typical Twilight Zone-ish twist stories of the type generally found in JIM.
The final story, 'Tales of Asgard: The Storm Giants' is a short story about Thor and Loki fighting some Storm Giants, that reads more like a Jack-and-the-Beanstalk type fairy tale than a Norse legend, but it's entertaining enough.
I would have like to see Marvel pull out all the stops for this 100th issue, but at least it's an above average issue.