Howard's ... fantasy world was very cosmetically different than Tolkien's work. His was a world that featured dying civilizations, ancient monsters and barbarians.
Tolkien's work featured
* dying civilizations
Gondor is the last remnant of Numenor, and a shadow of its former might. Its former capital is an abandoned ruin; its population is declining; its royal house extinct. Its great monuments crumble in the distance. But Gondor is alive; Arnor has collapsed entirely.
The Dwarves have a successful community going at Erebor, but their great capital of Moria is abandoned.
The Elves are still around and powerful, but also waning.
The Ents are a dead end.
The landscape is littered with the remnants of lost kingdoms - the Barrow-downs, Amon Sul, Moria, the Argonath, Amon Hen, the Path of the Dead, Isengard.
While Howard's landscape also features ancient ruins, it also includes mostly vigorous, growing societies.
* ancient monsters
the Barrow-Wight, the Watcher in the Water, the Balrog, Shelob, the Nazgul's flying mounts.
* barbarians
The Haradrim and Easterlings; the Dunlendings, and the Rohirrim. Yes, the Rohirrim. They're
nice barbarians, but still barbarians. For one things, AFAICT they're illiterate.